U.S. patent application number 14/101313 was filed with the patent office on 2015-06-11 for method and apparatus for directional centralized contention based period in a wireless communication system.
The applicant listed for this patent is Ismail Lakkis. Invention is credited to Ismail Lakkis.
Application Number | 20150163826 14/101313 |
Document ID | / |
Family ID | 43974126 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150163826 |
Kind Code |
A1 |
Lakkis; Ismail |
June 11, 2015 |
Method and Apparatus for Directional Centralized Contention Based
Period in a Wireless Communication System
Abstract
A method of communication includes allocating a portion of a
superframe centralized contention based period where the access
method is based on directional ALOHA. The centralized contention
based period is divided into equal time slots, and each sequential
set of N time slots forms a time cycle. During a time cycle, a
wireless device listens for requests from other wireless devices
while it changes its receiving direction from one time slot to
another.
Inventors: |
Lakkis; Ismail; (San Diego,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lakkis; Ismail |
San Diego |
CA |
US |
|
|
Family ID: |
43974126 |
Appl. No.: |
14/101313 |
Filed: |
December 9, 2013 |
Current U.S.
Class: |
370/336 |
Current CPC
Class: |
H01Q 3/24 20130101; H04W
72/0446 20130101; H04W 74/08 20130101; H04W 74/0816 20130101 |
International
Class: |
H04W 74/08 20060101
H04W074/08; H01Q 3/24 20060101 H01Q003/24; H04W 72/04 20060101
H04W072/04 |
Claims
1. A digital computer network comprising: a first transmitter
component residing on a first wireless device employing a sequence
of time slots paired with a plurality of transmit directions for
transmitting at least one request frame to a second wireless
device; a first receiver component residing on the first wireless
device configured for receiving at least one response frame from
the second wireless device; a second receiver component residing on
the second wireless device employing a different one of a plurality
of receive directions for each of the sequence of time slots to
listen for the at least one request frame transmitted by the first
transmitter; a second transmitter component residing on the second
wireless device configured for transmitting at least one response
frame to the first wireless device; and a digital computer system
comprising a memory for storing instructions and a processor for
executing the instructions for selecting a preferred set of uplink
and downlink directions for further communication between the first
wireless device and the second wireless device.
2. The digital computer network of claim 1, wherein a time cycle
comprises a plurality N of consecutive time slots, where N equals
the plurality of receive directions; and wherein the second
receiver component is configured for cycling through the plurality
of receive directions in each time cycle.
3. The digital computer network of claim 2, wherein each time cycle
has a time-cycle boundary selected by at least one of the first
wireless device and the second wireless device.
4. The digital computer network of claim 2, wherein each time cycle
has a time-cycle boundary selected by at least one of the first
wireless device and the second wireless device.
5. The digital computer network of claim 1, wherein the preferred
set comprises a preferred transmit direction for transmitting from
the second wireless device to the first wireless device, a
preferred receive direction for receiving transmissions from the
second wireless device to the first wireless device, and a
preferred transmit direction for transmitting from the first
wireless device to the second wireless device.
6. The digital computer network of claim 1, wherein the digital
computer system selects the preferred set based on measurements of
link quality.
7. The digital computer network of claim 1, wherein the digital
computer system performs at least one of a full double sweep and a
partial double sweep of all possible uplink and downlink direction
pairs when selecting the preferred set.
8. The digital computer network of claim 1, wherein the preferred
set comprises at least one of a set of directions having an optimal
link quality and a set of directions having a link quality above a
predetermined threshold.
9. The digital computer network of claim 1, wherein selecting the
preferred set comprises performing at least one of a full double
sweep and a partial double sweep of all possible uplink and
downlink direction pairs.
10. The digital computer network of claim 1, wherein selecting the
preferred set comprises selecting an uplink pair from beacon frames
and selecting a downlink pair during a C-CBP direction search.
11. The digital computer network of claim 1, wherein the digital
computer system is configured for maintaining a plurality of
downlink direction pairs, updating a link quality indicator
measurement for each of the plurality of downlink direction pairs,
and updating at least one of the set of uplink and downlink
directions.
12. The digital computer network of claim 1, configured for
performing at least one of directional slotted ALOHA and
directional cycle-based ALOHA.
13. The digital computer network of claim 1, configured for
performing at least one of authentication, association, direction
finding, direction tracking, communicating control frames, service
period reservation, communicating command frames, communicating
management frames, and communicating data frames.
14. A digital computer system, comprising: a transmitter configured
for selecting a sequence of time slots paired with a plurality of
transmit directions for transmitting at least one request frame to
at least one wireless device, the at least one wireless device
employing a different one of a plurality of receive directions for
each of the time slots; a receiver configured for listening for at
least one response frame transmitted by the at least one wireless
device; and a memory for storing instructions and a processor for
executing the instructions for selecting a preferred set of uplink
and downlink directions for further communication with the at least
one wireless device.
15. The digital computer system of claim 14, wherein selecting the
sequence further comprises employing a first transmit direction for
a first plurality N of the time slots, and a second transmit
direction for a second plurality N of the time slots, where N
equals the plurality of receive directions.
16. The digital computer system of claim 14, wherein the
transmitter is configured for employing a different transmit
direction for each of a plurality of time cycles when transmitting
the at least one request, wherein each of a plurality of time
cycles comprises a plurality N of consecutive time slots.
17. The digital computer system of claim 14, wherein each of the
time slots comprises a request frame slot, a first guard interval,
a response frame slot, and a second guard interval.
18. The digital computer system of claim 14, wherein the
transmitter employs a set of back-off numbers corresponding to
receive directions for determining back-off times for transmitting
request frames.
19. The digital computer system of claim 14, wherein the
transmitter employs an algorithm for selecting transmit directions
and time cycles for transmitting request frames.
20. The digital computer system of claim 14, configured to perform
at least one of directional slotted ALOHA and directional
cycle-based ALOHA.
21. A digital computer system, comprising: a receiver configured
for employing a different one of a plurality of receive directions
for each of a sequence of time slots to listen for at least one
transmitted request frame from a wireless device; a transmitter
configured for transmitting at least one response frame in response
to a received request frame; and a memory for storing instructions
and a processor for executing the instructions for selecting a
preferred set of uplink and downlink directions for further
communication with the wireless device.
22. The digital computer system of claim 21, wherein a time cycle
comprises a plurality N of consecutive time slots, where N equals
the plurality of receive directions; and wherein listening for the
at least one transmitted request frame comprises cycling through
the plurality of receive directions in each time cycle.
23. The digital computer system of claim 21, wherein the request
frame comprises a preferred transmit direction.
24. The digital computer system of claim 21, wherein selecting the
preferred set further comprises measuring an uplink link quality
indicator and transmitting the uplink link quality indicator to the
wireless device.
25. A digital computer system, comprising: a transmitter configured
for transmitting a request frame to a receiver employing a
plurality of receive directions to listen for the request frame;
and a memory for storing instructions and a processor for executing
the instructions for: generating a plurality of time cycle numbers,
each of the time cycle numbers being associated with one of the
receive directions and having a value within a predetermined
back-off window size; sequentially organizing the plurality of time
cycle numbers with respect to their values for producing a sequence
of time cycle numbers; and generating a sequence of time slot
numbers from the sequence of time cycle numbers and the plurality
of receive directions, the sequence of time slot numbers being used
by the transmitter to select time slots for transmitting the
request frame.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/911,732, filed Oct. 26, 2010, which claims
priority under 35 U.S.C. 119(e) to U.S. Provisional Application
Ser. No. 61/259,621, filed Nov. 9, 2009.
FIELD
[0002] Certain aspects of the present disclosure relate to wireless
communication, and particularly, to directional channel access in a
wireless communication system.
BACKGROUND
[0003] In one aspect of the related art, a wireless communication
system comprises a set of devices supporting at least one of a
single-carrier (SC) physical (PHY) layer and an Orthogonal
Frequency Division Multiplexing (OFDM) physical layer may be used
for millimeter wave communications, such as the systems envisioned
in the Institute of Electrical and Electronic Engineers (IEEE)
802.11.ad and IEEE 801.15.3c standards, and the Wireless Gigabit
Alliance (WGA). The PHY layer may be configured for millimeter wave
communications in the spectrum of 57 to 66 gigahertz (GHz), or
Ultra Wide Band (UWB) communications in the spectrum of 3.1 to 10.6
GHz.
[0004] To allow interoperability between devices or networks that
support either single-carrier or OFDM PHY modes, all devices
further support a common mode referred to as a control PHY.
Specifically, the common mode is a single-carrier base-rate mode
employed by both OFDM and single-carrier devices to facilitate
co-existence and interoperability between different devices and
different networks. The common mode may be employed for beaconing,
control, management, and communicating command and data frames
(packets).
[0005] In another aspect of the related art, devices typically
employ one or more Golay codes to provide spreading of different
fields of a packet. Complementary codes, first introduced by Golay
in M. Golay, "Complementary Series," IRE Transaction on Information
Theory, Vol. 7, Issue 2, April 1961, are sets of complementary
pairs of equally long, finite sequences of two kinds of elements.
These complementary pairs have the property that the number of
pairs of like elements with any given separation in one code is
equal to the number of unlike elements with the same separation in
the other code. The complementary codes first described by Golay
were pairs of binary complementary codes with elements +1 and -1,
wherein the sum of their respective aperiodic autocorrelation
sequence is zero everywhere, except for the center tap.
[0006] In a wireless network, such as a wireless personal area
network (WPAN) or a wireless local area network (WLAN), devices
typically use a slotted ALOHA protocol or a carrier sense multiple
access/collision avoidance (CSMA/CA) protocol to access the
wireless medium. However, these access methods do not perform well
when one or more devices use directional antenna patterns for their
transmissions and/or receptions.
[0007] Therefore, there is a need in the art for a directional
channel access protocol for devices that may have directional
antenna systems, such as phased antenna arrays, directional
antennas, or sectored antennas.
SUMMARY
[0008] Aspects disclosed herein may be advantageous to systems
employing millimeter-wave WPANs or WLANs (such as the WLANs
described by the IEEE802.11.ad, IEEE 802.11.ac and WGA protocols).
However, the disclosure is not intended to be limited to such
systems, as other applications may benefit from similar
advantages.
[0009] According to an aspect of the disclosure, a superframe
allocated by a first wireless device contains a centralized
contention period and a distributed contention period. During the
centralized contention period, the first device is part of any
communication link between a pair of wireless devices. The
distributed contention period may be used for peer-to-peer
communications between wireless devices. The distributed contention
period may be used for communication between the first device and
at least one other wireless device.
[0010] According to another aspect of the disclosure, a superframe
allocated by a first wireless device comprises a centralized
contention period that is further divided into fixed equal-size
time slots. The first device changes its receive antenna pattern
(also referred to as its direction) from one time slot to another
in a cyclic manner. Specifically, the first device uses a first
receive direction in the first time slot, a second receive
direction in the second time slot, and an N.sup.th receive
direction in the N.sup.th time slot. The first device reuses its
first receive direction in the (N+1).sup.th time slot, its second
receive direction in the (N+1).sup.th time slot, its N.sup.th
receive direction in the (2N).sup.th time slot, etc.
[0011] According to another aspect of the disclosure, a method of
communication is provided for accessing the centralized contention
period by one or more other wireless devices (e.g., a second
wireless device) to communicate with a first wireless device (a
master device) using a directional slotted ALOHA protocol. The
second device may transmit a frame on a time-slot boundary using a
transmit antenna pattern selected from a predetermined set of
transmit antenna patterns. The second device waits for a response
from the first device. The first device cycles through its
different receive patterns (i.e., directions) in each time
slot.
[0012] According to another aspect of the disclosure, a method of
communication is provided for allowing access to the centralized
contention period by one or more wireless devices (e.g., a second
wireless device) that communicate with a first wireless device
(e.g., a master device) using a directional slotted ALOHA protocol.
The second device maintains a set of N back-off window sizes equal
in number to the first device's number N of receive directions. The
second device may draw a set of N random numbers between one and
the back-off window size(s). Each random number indicates a
particular time cycle and time slot within the time cycle, which
provides a period of time that the second device waits before
transmitting the frame. Each time cycle comprises N time slots, and
the selection of a time slot in a time cycle may be determined by
the random number index in the set of the N random numbers.
[0013] According to another aspect of the disclosure, a method of
communication is provided for accessing a centralized contention
period that is used to communicate with a first wireless device (a
master device) using a directional cycle-based ALOHA protocol. A
second wireless device transmits a frame in the first time slot of
a time cycle using one of a plurality of transmit antenna patterns
from a set and waits for a response from the first device, which
uses a first receive direction in the first time slot. The second
device transmits the frame in the second time slot of a time cycle
using the same transmit antenna pattern and waits for a response
from the first device, which employs a second receive direction in
the second time slot. The second device employs successive (e.g.,
sequential) time slots of a time cycle for transmitting the frame
until it successfully decodes a response back from the first
device, or until it has transmitted the frame in all N time
slots.
[0014] According to another aspect of the invention, the
centralized contention period may be used for authentication,
association, service period requests, data communications, and/or
direction acquisition and tracking Each time slot has a fixed
duration, the time slot duration being at least equal to the
duration of a transmit request frame, a first guard period
(commonly known as an SIFS (Short Inter Frame Spacing)), the
duration of a response frame, and a second guard period (e.g., a
second SIFS).
[0015] According to another aspect of the disclosure, a
communications method comprises transmitting a service period
request (also known as a channel time allocation request) from a
second wireless device to a first wireless device, wherein the
service period request is transmitted using the directional slotted
ALOHA protocol; receiving a service period allocation granted by
the first device and transmitted using a second transmit pattern;
and transmitting at least one frame from the second device to a
destination device in the service period.
[0016] According to another aspect of the disclosure, a method of
communication comprises employing at least one of a full double
sweep and a partial double sweep for finding a pair of downlink
working directions.
[0017] The partial double sweep comprises transmitting a set of
request frames one at a time using a directional ALOHA protocol, in
a first transmit direction from a second wireless device to a first
wireless device. The first device changes its receive direction
from one time slot to another in a cyclic manner (i.e., the first
device repeats the same N receive directions in each time cycle).
The second device listens for a response from the first device. If
no response is detected, the second device sends a set of request
frames using a second transmit direction one at a time using the
directional ALOHA protocol, and the process of sending request
frames and listening for a response may be repeated for up to all
possible transmit directions or until the second device
successfully detects a response from the first device. The second
device uses the direction(s) for which it successfully decoded a
response from the first device as a working direction(s) that it
uses for further communications with the first device.
[0018] The full double sweep comprises transmitting a set of
request frames, one at a time using the directional ALOHA protocol,
in a first direction from the second device to the first device.
The first device changes its receive direction from one time slot
to another in a cyclic manner. The second device sends another set
of request frames in a second transmit direction to the first
device, one at a time using the directional ALOHA protocol. The
process of sending request frames is repeated for all transmit
directions of the second device. The second device selects the
direction(s) with the highest link quality indicator (LQI) as a
preferred direction(s) for communicating with the first device.
[0019] In accordance with one aspect of the invention, a wireless
system comprises means for selecting a sequence of time slots
paired with a plurality of transmit directions for transmitting at
least one request frame from a first wireless device to a second
wireless device; means for listening for the at least one request
frame at the second wireless device by employing a different one of
a plurality of receive directions in each of the time slots; means
for transmitting at least one response frame from the second
wireless device to the first wireless device; means for listening
for the at least one response frame at the first wireless device;
and means for selecting a preferred set of uplink and downlink
directions for further communication between the first wireless
device and the second wireless device. Means for selecting the
sequence of time slots may include, by way of example, but without
limitation, a digital computer system comprising a memory for
storing instructions and a processor for executing the
instructions. Means for listening may include, by way of example,
but without limitation, any wireless radio receiver employing
directional beam patterns and configured to detect, demodulate,
and/or decode received transmissions. Means for transmitting may
include, by way of example, but without limitation, any wireless
radio transmitter employing directional beam patterns and
configured for generating a response frame and other data signals,
and coupling data signals into a wireless communication channel.
Means for selecting a preferred set of uplink and downlink
directions may include, by way of example, but without limitation,
a digital computer system comprising a memory for storing
instructions and a processor for executing the instructions, and
may share one or more components used by the means for selecting
the sequence of time slots.
[0020] In accordance with another aspect of the invention, a
wireless device comprises means for selecting a sequence of time
slots paired with a plurality of transmit directions for
transmitting at least one request frame from the first wireless
device to a second wireless device, the second wireless device
employing a different one of a plurality of receive directions for
each of the time slots; means for listening for at least one
response frame transmitted by the second wireless device; and means
for selecting a preferred set of uplink and downlink directions for
further communication between the first wireless device and the
second wireless device. Means for selecting the sequence of time
slots may include, by way of example, but without limitation, a
digital computer system comprising a memory for storing
instructions and a processor for executing the instructions. Means
for listening may include, by way of example, but without
limitation, any wireless radio receiver employing directional beam
patterns and configured to detect, demodulate, and/or decode
received transmissions. Means for selecting a preferred set of
uplink and downlink directions may include, by way of example, but
without limitation, a digital computer system comprising a memory
for storing instructions and a processor for executing the
instructions, and may share one or more components used by the
means for selecting the sequence of time slots.
[0021] In accordance with another aspect of the invention, a
wireless device comprises means for employing a different one of a
plurality of receive directions for each of a sequence of time
slots to listen for at least one request frame transmitted by a
second wireless device; means for transmitting at least one
response frame to the second wireless device in response to a
received request frame; and means for selecting a preferred set of
uplink and downlink directions for further communication between
the first wireless device and the second wireless device. Means for
employing a different one of a plurality of receive directions for
each of a sequence of time slots to listen for at least one request
frame transmitted by a second wireless device may include, by way
of example, but without limitation, any wireless radio receiver
employing directional beam patterns and configured to detect,
demodulate, and/or decode received transmissions. Means for
transmitting may include, by way of example, but without
limitation, any wireless radio transmitter employing directional
beam patterns and configured for generating a response frame and
other data signals, and coupling data signals into a wireless
communication channel. Means for selecting a preferred set of
uplink and downlink directions may include, by way of example, but
without limitation, a digital computer system comprising a memory
for storing instructions and a processor for executing the
instructions.
[0022] In accordance with another aspect of the invention, a
wireless device comprises means for generating a plurality of time
cycle numbers, the plurality of time cycle numbers being equal to a
plurality of receive directions employed by a second wireless
device, each of the time cycle numbers being associated with one of
the receive directions and having a value within a predetermined
back-off window size; means for sequentially organizing the
plurality of time cycle numbers with respect to their values for
producing a sequence of time cycle numbers; means for generating a
sequence of time slot numbers from the sequence of time cycle
numbers and the plurality of receive directions, the sequence of
time slot numbers being used to select time slots for transmitting
a frame to the second wireless device. Means for generating the
plurality of time cycle numbers, means, means for sequentially
organizing the plurality of time cycle numbers, and means for
generating the sequence of time slot numbers may include, by way of
example, but without limitation, a digital computer system
comprising a memory for storing instructions and a computer
processor for executing the instructions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] So that the manner in which the above-recited features of
the present disclosure can be understood in detail, a more
particular description, briefly summarized above, may be had by
reference to aspects, some of which are illustrated in the appended
drawings. It is to be noted, however, that the appended drawings
illustrate only certain typical aspects of this disclosure and are
therefore not to be considered limiting of its scope, for the
description may admit to other equally effective aspects.
[0024] FIG. 1 illustrates a wireless communication system in
accordance with certain aspects of the present disclosure.
[0025] FIG. 2 illustrates various components that may be utilized
in a wireless device in accordance with certain aspects of the
present disclosure.
[0026] FIG. 3 illustrates an example transceiver that may be used
within a wireless communication system in accordance with certain
aspects of the present disclosure.
[0027] FIG. 4A illustrates a conventional superframe structure in
accordance with certain aspects of the present disclosure.
[0028] FIG. 4B illustrates a frame structure in accordance with
certain aspects of the present disclosure.
[0029] FIG. 5A illustrates a directional beacon period in
accordance with certain aspects of the present disclosure.
[0030] FIG. 5B illustrates a contention period using a slotted
ALOHA protocol according to certain aspects of the present
disclosure.
[0031] FIG. 6A illustrates a superframe structure in accordance
with certain aspects of the present disclosure.
[0032] FIG. 6B illustrates a centralized contention period using a
directional ALOHA protocol according to certain aspects of the
present disclosure.
[0033] FIG. 7A illustrates a time-slot structure in accordance with
certain aspects of the present disclosure.
[0034] FIG. 7B illustrates a time-cycle structure in accordance
with certain aspect of the present disclosure.
[0035] FIG. 8 illustrates a directional slotted ALOHA protocol in
accordance with certain aspect of the present disclosure.
[0036] FIG. 9A illustrates an operation for transmitting a beacon
frame that may be used within a wireless communication system in
accordance with certain aspects of the present disclosure.
[0037] FIG. 9B illustrates components configured for performing the
operations illustrated in FIG. 9A.
[0038] FIG. 9C illustrates operations for processing a beacon frame
at the receiver in accordance with certain aspects of the present
disclosure.
[0039] FIG. 9D illustrates components configured for performing the
operations illustrated in FIG. 9C.
[0040] FIG. 10A illustrates a method for performing a directional
slotted-ALOHA protocol with respect to certain aspects of the
present disclosure.
[0041] FIG. 10B illustrates components of a system configured for
performing the method illustrated in FIG. 10A.
[0042] FIG. 10C illustrates a method for processing a frame at the
receiver in accordance with certain aspects of the present
disclosure.
[0043] FIG. 10D illustrates an apparatus configured for performing
the method illustrated in FIG. 10C.
[0044] FIG. 11A illustrates a method for retransmitting a frame
using a directional slotted ALOHA protocol in accordance with
certain aspects of the present disclosure.
[0045] FIG. 11B illustrates an apparatus configured for performing
the method illustrated in FIG. 11A.
[0046] FIG. 12A illustrates a method for processing a frame
transmitted using a directional slotted ALOHA protocol at a
receiver in accordance with certain aspects of the present
disclosure.
[0047] FIG. 12B illustrates an apparatus configured for performing
the method illustrated in FIG. 12A.
[0048] FIG. 13A illustrates a method for performing a double sweep
using a directional slotted ALOHA protocol in accordance with
certain aspects of the present disclosure.
[0049] FIG. 13B illustrates an apparatus configured for performing
the method illustrated in FIG. 13A.
DETAILED DESCRIPTION
[0050] Various aspects of the disclosure are described more fully
hereinafter with reference to the accompanying drawings. This
disclosure may, however, be embodied in many different forms and
should not be construed as limited to any specific structure or
function presented throughout this disclosure. Rather, these
aspects are provided so that this disclosure will be thorough and
complete, and will fully convey the scope of the disclosure to
those skilled in the art. Based on the teachings herein one skilled
in the art should appreciate that the scope of the disclosure is
intended to cover any aspect of the disclosure disclosed herein,
whether implemented independently of or combined with any other
aspect of the disclosure. For example, an apparatus may be
implemented or a method may be practiced using any number of the
aspects set forth herein. In addition, the scope of the disclosure
is intended to cover such an apparatus or method which is practiced
using other structure, functionality, or structure and
functionality in addition to or other than the various aspects of
the disclosure set forth herein. It should be understood that any
aspect of the disclosure disclosed herein may be embodied by one or
more elements of a claim.
[0051] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any aspect described herein as
"exemplary" is not necessarily to be construed as preferred or
advantageous over other aspects.
[0052] Although particular aspects are described herein, many
variations and permutations of these aspects fall within the scope
and spirit of the disclosure. Although some benefits and advantages
of the preferred aspects are mentioned, the scope of the disclosure
is not intended to be limited to particular benefits, uses, or
objectives. Rather, aspects of the disclosure are intended to be
broadly applicable to different wireless technologies, system
configurations, networks, and transmission protocols, some of which
are illustrated by way of example in the figures and in the
following description of the preferred aspects. The detailed
description and drawings are merely illustrative of the disclosure
rather than limiting, the scope of the disclosure being defined by
the appended claims and equivalents thereof. AN EXAMPLE WIRELESS
COMMUNICATION SYSTEM
[0053] The techniques described herein may be used for various
broadband wireless communication systems, including communication
systems that are based on a single carrier transmission and OFDM.
Aspects disclosed herein may be advantageous to systems employing
Ultra Wide Band (UWB) signals including millimeter-wave signals,
Code Division Multiple Access (CDMA) signals, and OFDM. However,
the present disclosure is not intended to be limited to such
systems, as other coded signals may benefit from similar
advantages.
[0054] FIG. 1 illustrates an exemplary wireless communication
system 100 in which aspects of the present disclosure may be
employed. The wireless communication system 100 may be a broadband
wireless communication system compatible with the IEEE 802.11 and
802.15. The wireless communication system 100 may provide
communication for a number of Basic Service Sets (BSSs) 102, each
of which may be serviced by a Service Access Point (SAP) 104. A SAP
104 may be a fixed station or a mobile station that communicates
with Stations (STAs) 106. A BSS 102 may alternatively be referred
to as cell, piconet or some other terminology. The SAP 104 may
alternatively be referred to as a base station, a piconet
controller, a Node B, a wireless device, a master device, or some
other terminology.
[0055] FIG. 1 depicts various stations 106 dispersed throughout the
system 100. The stations 106 may be fixed (i.e., stationary) or
mobile. Each STA of the plurality of STAs 106 implements a MAC and
PHY interface to the wireless medium of the network 100. The STAs
106 may alternatively be referred to as remote stations, access
terminals, terminals, subscriber units, mobile stations, wireless
devices, user equipment, etc. The STAs 106 may be wireless devices,
such as cellular phones, personal digital assistants (PDAs),
handheld devices, wireless modems, laptop computers, personal
computers, etc.
[0056] Under IEEE 802.11 and 802.15, one STA assumes the role of a
coordinator (master) of the BSS. This coordinating STA is referred
to as a Service Access Point (SAP) and is illustrated in FIG. 1 as
the SAP 104. Thus, the SAP 104 may include the same station
functionality of the plurality of other stations (STAs 106), but
provides coordination and management for the network. For example,
the SAP 104 provides services, such as basic timing for the network
100 using a beacon; and management of any Quality of Service (QoS)
requirements, power-save modes, and network access control. A
wireless device with similar functionality as described for the SAP
104 in other systems may be referred to as an piconet controller, a
base station, a base transceiver station, a station, a terminal, a
node, an access terminal acting as an access point, or some other
suitable terminology. The SAP 104 coordinates the communication
between the various stations (STAs 106) in the network 100 using a
frame structure referred to as a superframe. Each superframe is
bounded in time by beacon periods. The SAP 104 may be coupled to a
system controller to communicate with other networks or other
SAPs.
[0057] A variety of algorithms and methods may be used for
transmitting information in the wireless communication system 100
between the SAPs 104 and the STAs 106 and between the STAs 106
themselves. For example, signals may be communicated between the
SAPs 104 and the STAs 106 in accordance with a CDMA technique and
signals may be sent and received between STAs 106 in according with
an OFDM technique. If this is the case, the wireless communication
system 100 may be referred to as a hybrid CDMA/OFDM system.
[0058] A communication link that facilitates transmission from an
SAP 104 to an STA 106 may be referred to as a downlink (DL) 108,
and a communication link that facilitates transmission from an STA
106 to an SAP 104 may be referred to as an uplink (UL) 110.
Alternatively, a downlink 108 may be referred to as a forward link
or a forward channel, and an uplink 110 may be referred to as a
reverse link or a reverse channel. When two STAs communicate
directly with each other, a first STA will act as the master of the
link, and the link from the first STA to the second STA will be
referred to as the downlink 112, and the link from the second STA
to the first STA will be referred to as the uplink 114.
[0059] A BSS 102 may be divided into multiple sectors. A sector 116
is a physical coverage area within the BSS 102. SAPs 104 within the
wireless communication system 100 may utilize antennas that
concentrate the flow of power within a particular sector 116 of the
BSS 102. Such antennas may be referred to as directional
antennas.
[0060] FIG. 2 illustrates various components that may be utilized
in a wireless device 210 employed within the wireless communication
system 100. The wireless device 210 is an example of a device that
may be configured to implement the various methods described
herein. The wireless device 202 may be an SAP 104 or an STA
106.
[0061] The wireless device 202 may include a processor 204 that
controls operation of the wireless device 202. The processor 204
may also be referred to as a central processing unit (CPU). Memory
206, which may include one or both read-only memory (ROM) and
random access memory (RAM), provides instructions and data to the
processor 204. A portion of the memory 206 may also include
non-volatile random access memory (NVRAM). The processor 204
typically performs logical and arithmetic operations based on
program instructions stored within the memory 206. The instructions
in the memory 206 may be executable to implement the methods
described herein.
[0062] The wireless device 202 may also include a housing 208 that
may include a transmitter 210 and a receiver 212 to allow
transmission and reception of data between the wireless device 202
and a remote location. The transmitter 210 and receiver 212 may be
combined into a transceiver 214. An antenna 216 may be attached to
the housing 208 and electrically coupled to the transceiver 214.
The wireless device 202 may include one or more wired peripherals
224 such as USB, HDMI, or PCIE. The wireless device 202 may also
include (not shown) multiple transmitters, multiple receivers,
multiple transceivers, and/or multiple antennas.
[0063] The wireless device 202 may also include a signal detector
218 that may be used to detect and quantify the level of signals
received by the transceiver 214. The signal detector 218 may detect
such signals as total energy, energy per subcarrier per symbol,
power spectral density, and/or other signal measurements that are
known in the art. The wireless device 202 may also include a
digital signal processor (DSP) 220 for processing signals.
[0064] The various components of the wireless device 202 may be
coupled together by a bus system 222, which may include a power
bus, a control signal bus, and a status signal bus, in addition to
a data bus.
[0065] FIG. 3 illustrates an exemplary transmitter 302 that may be
used within a wireless communication system 100 that utilizes CDMA
or some other transmission technique. Portions of the transmitter
302 may be implemented in the transmitter 210 of a wireless device
202. The transmitter 302 may be implemented in a base station 104
for transmitting data 330 to a user terminal 106 on a downlink 108.
The transmitter 302 may also be implemented in a station 106 for
transmitting data 330 to a service access point 104 on an uplink
110.
[0066] Data 306 to be transmitted are shown being provided as input
to a forward error correction (FEC) encoder 308. The FEC encoder
308 encodes the data 306 by adding redundant bits. The FEC encoder
308 may encode the data 306 using a convolutional encoder, a Reed
Solomon encoder, a Turbo encoder, a low density parity check (LDPC)
encoder, etc. The FEC encoder 308 outputs an encoded data stream
310. The encoded data stream 310 is input to a mapper 314. The
mapper 314 may map the encoded data stream onto constellation
points. The mapping may be done using some modulation
constellation, such as binary phase-shift keying (BPSK), quadrature
phase-shift keying (QPSK), 8 phase-shift keying (8PSK), quadrature
amplitude modulation (QAM), constant phase modulation (CPM), etc.
Thus, the mapper 312 may output a symbol stream 314, which may
represents one input into a block builder 310. Another input in the
block builder 310 may include one or more spreading codes produced
by a spreading code generator 318.
[0067] The block builder 310 may be configured for partitioning the
symbol stream 314, into sub-blocks and creating OFDM/OFDMA symbols
or single-carrier sub-blocks. The block builder 310 may append each
sub-block with a guard interval, a cyclic prefix, or a spreading
sequence from the spreading codes generator 318. Furthermore, the
sub-blocks may be spread by one or multiple spreading codes from
the spreading code generator 318.
[0068] Output signal 320 may be pre-pended by a preamble 322
generated from one or more spreading sequences from the spreading
code generator 324. The output stream 326 may then be converted to
analog and up-converted to a desired transmit frequency band by a
radio frequency (RF) front end 328, which may include a mixed
signal section and an analog section. An antenna 330 transmits the
resulting signal 332.
[0069] FIG. 3 illustrates an exemplary receiver 304 that may be
used within a wireless device 202 that uses CDMA and/or OFDM/OFDMA.
Portions of the receiver 304 may be implemented in the receiver 212
of a wireless device 202. The receiver 304 may be implemented in a
station 106 for receiving data 306 from a service access point 104
on a downlink 108. The receiver 304 may also be implemented in a
base station 104 for receiving data 306 from a user terminal 106 on
an uplink 110.
[0070] The transmitted signal 332 is shown traveling over a
wireless channel 334. When a signal 332' is received by an antenna
330', the received signal 332' may be down-converted to a baseband
signal by an RF front-end 328' which may include a mixed signal and
an analog portion. Preamble detection and synchronization component
322' may be used to establish timing, frequency and channel
synchronization using one or multiple correlators that correlate
with one or multiple spreading codes generated by a spreading code
generator 324'.
[0071] The output of the RF front end block 328' is input to the
frequency and timing correction component 326' along with the
synchronization information from component 322'. The outputs from
components 326' and 322' are input to a block detection component
316'. When OFDM/OFDMA is used, the block detection may include
cyclic prefix removal and fast Fourier transform (FFT). When
single-carrier transmissions are used, the block detection may
include de-spreading and equalization.
[0072] A de-mapper 312' may perform the inverse of the symbol
mapping operation performed by the mapper 312, thereby outputting
soft and/or hard decisions 310'. The soft and/or hard decisions
310' are input to the FEC decoder 308', which provides a stream of
data estimates 306'. Ideally, this data stream 306' corresponds to
the data 306 that was input to the transmitter 302.
[0073] The wireless system 100 illustrated in FIG. 1 may be a
UWB/millimeter wave system operating in the band including the
57-64 GHz unlicensed band specified by the Federal Communications
Commission (FCC).
Superframe Structure
[0074] FIG. 4A illustrates a superframe 400 used for SAP timing in
the network 100. In general, a superframe is a basic time-division
structure containing a beacon period (BP) 410, a contention based
period (CBP) 420, and a channel time allocation (CTAP) period 430,
also known as service periods (SPs). The superframe is also known
as the beacon time (BT) or beacon interval (BI). In the superframe
400, a beacon period (BP) 410 is provided during which an SAP such
as the SAP 104 sends beacon frames.
[0075] A Contention Based Period (CBP) 420 is used to communicate
command, control, management, and data frames either between the
SAP 104 and at least one of the plurality of STAs 106 in the
network 100, or between any set of STAs 106 in the network 100. The
access method for the CBP 420 may be based on a slotted ALOHA or a
carrier sense multiple access with collision avoidance (CSMA/CA)
protocol.
[0076] A Channel Time Allocation Period (CTAP) 430, which is based
on a Time Division Multiple Access (TDMA) protocol, is provided by
the SAP 104 to allocate time for the plurality of STAs 106 to use
the channels in the network 100. Specifically, the CTAP is divided
into one or more time periods (of different sizes), referred to as
Channel Time Allocations (CTAs). The CTAs, also known as Service
Periods (SPs), are typically allocated by the SAP 104 to pairs of
stations, one pair of stations to a CTA. Thus, the access mechanism
for CTAs is TDMA-based.
[0077] FIG. 4B shows an exemplary frame structure 450 that may be
used for a single-carrier, OFDM, or common-mode frame. As used
herein, the term, frame, may also be used interchangeably with the
term, packet. The frame structure 450 includes a preamble 452, a
header 454, and a packet payload 456. The common mode may use Golay
codes for all three fields, i.e., for the preamble 452, the header
454 and the packet payload 456. The common-mode signal uses Golay
spreading codes with chip-level/2-BPSK modulation to spread the
data therein. The header 454, which is a physical layer convergence
protocol (PLCP) conforming header, and the packet payload 456,
which is a physical layer service data unit (PSDU), includes
symbols spread with a Golay code of length 32 or 64. Various frame
parameters, including, by way of example, but without limitation,
the number of Golay-code repetitions and the Golay-code lengths,
may be adapted in accordance with various aspects of the frame
structure 450. In one aspect, Golay codes employed in the preamble
may be selected from length-64 or length-128 Golay codes. Golay
codes used for data spreading may comprise length-32 or length-64
Golay codes.
[0078] Referring to FIG. 4B, the preamble 452 includes a packet
sync sequence field 458, an optional start frame delimiter (SFD)
field 460, and a channel-estimation sequence field 462.
[0079] The packet sync sequence field 458 is a repetition of ones
(or a repetition of minus ones, or an alternating sequence of ones
and minus ones) spread by one of the length-128 complementary Golay
codes (a128, b128) as represented by codes 464-1 to 464-Q in FIG.
4B. The SFD field 460 comprises a specific code such as {-1, +1}
that is spread by one of the length-128 complementary Golay codes
(a128, b128), as represented by codes 466-1 and 466-2 in FIG. 4B.
The CES field 462 may be spread using a pair of length-256
complementary Golay codes (a256, b256), such as represented by
codes 458-1 and 458-2, and may further comprise a cyclic postfix
458-3, which is a length-128 Golay code. The CES field 462 may
further comprise a cyclic prefix (not shown), where CP may be used
as a Cyclic Prefix or Postfix. A cyclic postfix for code a256
(depicted by 458-1) is shown as CP128 458-3 and is a copy of the
first 128 chips of a256 (458-1). The sync field 458 is typically
used for AGC (Automatic Gain Control) setting, antenna selection,
DC offset removal, packet detection, timing, and frequency and
channel acquisition. The SFD field 460 may be used to indicate the
end of the sync field 458. The CES field 462 is typically used for
multipath channel estimation and fine frequency estimation.
[0080] In one aspect of the disclosure, a dual-mode millimeter wave
system employing single-carrier modulation and OFDM is provided
with a single-carrier common-mode signaling. The common mode, also
known as control PHY (Physical layer), is a single-carrier mode
used by both single-carrier and OFDM devices for beaconing,
signaling (such as control and management), beamforming, and
base-rate data communications.
Directional Aloha Protocol
[0081] In typical systems, an SAP transmits a single beacon frame
in the beacon period (BP) 410, such as depicted in FIG. 4A. This is
the case in IEEE 802.11 where a SAP transmits the beacon using a
single antenna pattern that covers the region of space of interest.
In millimeter wave systems, such as the systems being considered in
IEEE 802.11 ad and WGA, stations may not be omni-capable on
transmission or reception. That is, stations might not be able to
cover the region of space of interest in a single transmission or
reception pattern. Such stations are referred to herein as
directional stations. An omni-capable device is a special case of a
directional station with a single direction. Directional STAs
include STAs that use switched antennas, sectored antennas, and/or
phased antenna arrays. In what follows, antenna patterns are
referred to as directions, and it should be understood that an
antenna direction (e.g., an antenna pattern) does not necessarily
imply a specific geometric coverage, such as antenna beams. An
antenna direction (e.g., a pattern) may take any three-dimensional
geometric shape, including, but not limited to, typical beam and
sectored patterns. Furthermore, a station may use different
directions for transmission and reception.
[0082] According to one aspect of the invention, during the beacon
interval 410 in FIG. 4A, a directional SAP transmits a plurality of
beacon frames using a plurality of transmit antenna patterns,
denoted by indices #1 to #M. This is further illustrated in FIG.
5A, wherein an SAP with M transmit patterns may transmit M beacon
frames, wherein the first beacon frame 510-1 is transmitted in a
first transmit direction #1, and the second beacon frame 510-2 is
transmitted in a second transmit direction #2, and the M.sup.th
beacon frame 510-M is transmitted in a M.sup.th transmit direction
#M. The beacon packets may be separated by Minimum InterFrame
Spacing (MIFS) guard intervals, such as represented by 520-1 to
520-M. Each beacon frame contains one or two counters (typically in
the header of the frame) containing information about the index of
the current beacon frame and the total (or remaining) number of
beacon frames M. With the exception of the content of the counters,
the content of all beacon frames may be identical.
[0083] For an SAP that is omni-capable on transmission (i.e., an
SAP with a single antenna pattern covering the region of interest),
M=1. For an SAP with sectorized antennas, M is the number of
sectors that the SAP is able to support. Similarly, when an SAP is
provided with switching transmit diversity antennas, M may
represent the number of transmit antennas in the SAP. Various
approaches to the structure of the Q-omni beacon frame may be
used.
[0084] The following disclosure relates to the general case of
stations (STAs), including SAPs, having transmit directions and
receive directions that may be different (referred to as asymmetric
STAs). Stations having identical transmit directions and receive
directions (referred to as symmetric STAs) are a special case.
[0085] As discussed above, a SAP broadcasts a set of M beacon
frames, typically in every superframe. Each beacon frame contains
all timing information about the superframe and, optionally,
information about some or all of the STAs that are members of the
BSS, including the beamforming capabilities of each STA. The STA
beamforming capabilities are obtained by the SAP during
association. An STA beamforming capability includes a number of
transmit and receive directions. An STA may use a different number
of transmit and receive directions for different tasks. For
example, the number of directions could be a number of antennas for
an STA with switched antennas, a number of sectors for an STA with
sectored antennas, or a number of coarse patterns for an STA with a
phase antenna array. A phased antenna array can generate a set of
patterns that may overlap, each pattern covering a part of the
region of the space of interest.
[0086] The following notation is used to clarify different aspects
of the disclosure. Let M and N be the total number of SAP's
transmit and receive antenna patterns, respectively, and let P and
Q be the total number of an STA's transmit and receive antenna
patterns respectively. As mentioned above, the number of directions
M, N, P, and Q may be changed. As an example, an STA may use P=2
directions during association and P=16 directions in a CTAP.
Furthermore, an STA may initially use a coarse number of broad
directions and adapt either or both the directions and the number
of directions to provide a set of fine directions.
[0087] An STA may perform the following steps in order to associate
(i.e., become a member of the BSS) with the SAP. First, the STA
searches for a beacon from the SAP. The STA then detects at least
one of the M directional beacon frames and acquires knowledge of
the superframe timing, the number of the SAP's transmit and receive
directions (i.e. M and N), duration of the CBP, and, optionally,
the possible capabilities of each of the STA members. In an aspect
of the disclosure, the STA acquires and tracks the best SAP
transmit direction by measuring a link quality indicator (LQI) from
all K directional beacon packets transmitted by the SAP. In one
aspect of the disclosure, the LQI is a metric of the quality of the
received signal. Examples of an LQI include, but are not limited
to, an RSSI (Received Signal Strength Indicator), an SNR (Signal to
Noise Ratio), an SNIR (Signal to Noise and Interference Ratio), an
SIR (Signal to Interference Ratio), a preamble detection, a BER
(Bit Error Rate), and a PER (Packet Error Rate).
[0088] According to one aspect of the disclosure, an STA may detect
a beacon packet by sweeping over its set of N receive directions
over one or more superframes. Upon detection of at least one of the
beacon packets, the STA acquires a vast amount of information. For
example, the STA may acquire knowledge of the following: a) the
SAP's number of transmit and receive directions during beaconing
(i.e., M and N); b) the index of SAP's preferred transmit direction
(e.g., the beacon packet with the highest LQI) from the SAP to the
STA, referred to as the SAP's transmit direction number m.
Direction number m is acquired by the STA by sorting the LQIs from
the M beacon frames transmitted by the SAP in different directions
and received by the STA using its Q receive directions. There are
M.times.Q combinations in total, and one combination yields a best
LQI. Alternatively, the STA may use the direction corresponding to
the first beacon frame it successfully detects as its preferred
direction; c) the index of the STA's preferred receive direction
when listening to the SAP. The STA's preferred receive direction is
referred to as direction q; d) the list of devices that are members
of the current BSS, and some or all of their capabilities in terms
of PHY support (single carrier support or OFDM support, data rates,
number of transmit and receive directions, etc.); e) the structure
and duration of different fields of the superframe, such as the
start time of CBP, duration of the CBP, superframe duration, etc.;
and f) the time allocations of SPs in the CTAP.
[0089] Upon detection of the beacon, the STA goes through the
association process to become a member of the BSS. After
association, the STA may exchange data packets with another STA or
with the SAP in accordance with one of two procedures. In
accordance with a first procedure, the STA may access the
contention-based period using a slotted ALOHA protocol or a carrier
sense multiple access with collision avoidance CSMA/CA protocol in
a manner similar to that specified in the IEEE 802.11 protocol. In
accordance with a second procedure, the STA requests a service
period (SP) from the SAP for the purpose of exchanging data packets
with another STA. If the request is accepted by the SAP, the SAP
grants access to the demanding STA and broadcasts a time allocation
in the beacon. The SAP may provide information about the source STA
and address STA(s). The source and destination STAs may then
exchange data packets in the dedicated time allocated service
period.
[0090] The association process involves transmitting an association
request from the STA to the SAP, and transmitting an association
response from the SAP to the STA. This process may involve
exchanges of many frames before the STA is considered to be
associated. Furthermore, an STA might have to be authenticated
prior to association. Authentication may be part of the association
process.
[0091] For networks such as IEEE 802.11, the SAP and STAs have a
single transmit antenna pattern, and the association process is
relatively simple and straightforward. IEEE 802.11 uses a CSMA/CA
protocol. To clarify the association process, a simple slotted
ALOHA protocol is shown in FIG. 5B. The contention based period is
divided into equal size time slots 560-1 to 560-T, where the slot
duration encompasses the duration of an association request frame
from the STA, plus the duration of a guard time, such as a first
SIFS, plus the duration of an association response frame from the
SAP, plus the duration of another guard time (such as a second
SIFS). An STA may send a request only at the beginning of a time
slot. If the STA does not detect a response after a SIFS guard
time, it regards the request as unsuccessful. For example, a
collision may have occurred with a request sent by another STA to
the SAP during the same time slot. In this case, the STA may
retransmit the request in a future slot determined by some
probability law calculation. Typically, a binary exponential
back-off procedure is used. A STA draws a random number R.sub.1
between 1 and W=2.sup.s (where W is referred to here as initial
back-off window size), and transmits a request frame in time-slot
number R.sub.1. If the request is unsuccessful, then the back-off
window size is doubled and the STA draws another random number
R.sub.2 between 0 and 2.sup.(q+1) and retransmits the request in
time-slot number R.sub.1+R.sub.2. Every time the request is
unsuccessful, the back-off window size is doubled until it reaches
a threshold 2.sup.S, after which the back-off window is constant.
If the maximum back-off window is reached and the number of
transmission trials exceeds a predetermined number, the station
ceases its attempts to transmit the frame. On the other hand, if
the transmission is successful, the back-off window size is reset
back to 2.sup.s for the next transmission.
[0092] For directional STAs and/or SAPs, the previously described
slotted ALOHA procedure may not perform well, especially when an
STA does not know which direction to use for transmissions to the
SAP and the SAP does not know which direction to use for reception.
The same problem occurs with CSMA/CA, since good STA-to-SAP and
SAP-to-STA directions are not known at either side of the link.
Furthermore, the hidden-node problem is worse, since stations
cannot hear each other due to their directional antenna patterns.
In addition, the problem is more severe if the contention based
period is used for direction finding, authentication, association,
service period (time allocation) request, data frame exchange
between peer-to-peer STAs, and data frame exchanges between the STA
and SAP.
[0093] According to one aspect of the invention, the contention
based period is divided into two portions, a centralized contention
based period (C-CBP) 620 and a distributed contention based period
(D-CBP) 630, such as shown in FIG. 6A. In the C-CBP 620, the SAP is
a party to any communication. That is, communications occurs
between the SAP and other STAs. In the D-CBP, the SAP is not
necessarily part of every communication. That is, communications
may occur between two STAs, and not the SAP.
[0094] In the following, a frame transmission from an STA to the
SAP is referred to as a request frame, and frame transmission from
the SAP to an STA is referred to as a response frame.
[0095] In one aspect of the invention, the centralized contention
based period is divided into equal-size slots, such as shown in
FIG. 6B. A time slot is further illustrated in FIG. 7A. At the
beginning of a time slot, an STA may transmit a request frame 710
to the SAP. After a guard interval (SIFS) 720, the SAP transmits a
response frame 730 to the STA, and a guard interval SIFS follows
before another request is allowed. The slot duration should be
longer than the maximum duration of a request frame, plus a first
SIFS, plus the maximum duration of a response frame, plus a second
SIFS. In the following, the combination of request frame and
response frame is referred to as a transaction.
[0096] In FIG. 6B, the centralized based contention period (C-CBP)
is divided into equal-size time slots 664-1-1 to 664-S-N. In the
first time slot 664-1-1, the SAP selects receive direction
(pattern) number 1 and listens for any request frame transmitted by
an STA. If the SAP detects a request frame, the SAP responds by
transmitting a response frame after a SIFS guard interval. In the
second time slot 664-1-2, the SAP listens in receive direction
number 2. This process is repeated for all N SAP receive
directions. In the N.sup.th slot 664-N, the SAP employs receive
direction number N. In the (N+1).sup.th time slot 664-2-1, the SAP
listens in receive direction number 1. In the (N+2).sup.th time
slot 664-2-2, the SAP listens in direction number 2, and in the
(2N).sup.th time slot 664-2-N, the SAP listens while using receive
direction number N. In summary, the SAP uses its N receive
directions in a cyclic manner. Therefore during the t.sup.th time
slot, the SAP uses its receive direction number [(t-1) mod N]+1. A
set of N consecutive time slots wherein the SAP cycles (i.e.,
sweeps) through its receive directions 1 to N is referred to as a
time cycle, such as illustrated by time cycles 662-1 to 662-S.
[0097] According to one aspect of the invention, an SAP may specify
fixed time-cycle boundaries where the first time cycle boundary
coincides with the first time slot in the C-CBP. According to
another aspect of the invention, an SAP may leave the choice of
time-cycle boundaries to different STAs. As an example, an STA
might choose a time cycle as time slots 664-1-2 to and including
664-2-1. That is, from an STA's perspective, a time cycle comprises
N consecutive time slots, such as time slots 1 to N, or time slots
2 to N+1, or time slots 3 to N+2, etc.
[0098] Before using the C-CBP, an STA acquires the beacon, such as
described previously. After beacon detection, an SAP acquires
knowledge of its preferred SAP transmit direction number m (i.e.,
the preferred SAP-to-STA transmit direction). The STA determines
its preferred receive direction number q by listening to the SAP.
Therefore, before using the C-CBP, an STA is equipped with the
SAP's preferred transmit direction m and its preferred receive
direction n. The values m and q are the preferred uplink pair of
directions.
[0099] According to one aspect of the invention, an STA uses the
same transmit direction for each set of N consecutive time slots.
This set of N-consecutive time slots may (but not necessarily) be
aligned with a time cycle, such as cycles 662-1 to 662-S. For
example, if there is only one STA in the network, the STA may
transmit a first request frame using its transmit direction #1 in a
time slot number 1 and then waits for a response. During this time
slot, the SAP uses its receive direction number 1. If no response
is detected by the STA, one of the reasons may be that the
combination of STA transmit direction number 1 and SAP receive
direction number 1 does not have enough LQI. The STA transmits a
second request frame in time-slot number 2 while still using its
transmit direction number 1, but the SAP employs its receive
direction number 2. If the STA does not detect a response, it
continues transmitting request frames using the same transmit
direction number 1 for each of the N time slots or until a response
is detected. If no response is received by the STA after
transmitting in the N time slots, the STA uses transmit direction
number 2 for the next N time slots or until a response is received.
This process may be repeated for each of the STA's transmit
directions or until a response is received. Such a process is
referred to as a double sweep, wherein the SAP sweeps (i.e.,
changes its direction) on a time-slot basis (i.e., the SAP's
receive direction changes every time slot). The STA sweeps on a
cycle basis, that is, it changes its transmit direction every time
cycle (i.e., N time slots). This double sweep is illustrated in
FIG. 7B, which shows a cycle of N time slots 760-1 to 760-N. During
this cycle, the STA uses the same transmit direction number PC
during all time slots 760-1 to 760-N, and the SAP changes its
receive direction from one time slot to another and cycles through
all of its receive directions 1 to N.
[0100] According to another aspect of the invention, each request
frame sent by the STA comprises information regarding the SAP's
preferred transmit direction m. As described above, the STA
determines the SAP's preferred transmit direction from the beacon
detection and monitoring stage. Once the SAP detects and decodes a
request frame sent by an STA, it determines which transmit
direction to use for transmitting the response frame to the
STA.
[0101] Once a response frame is detected by the STA, the STA and
SAP have a working pair of directions in both downlink and uplink.
That is, the STA determines a working transmit direction toward the
SAP and a preferred receive direction when receiving from the SAP.
The STA's working transmit direction is not necessarily the best
direction. Rather, it may be the first direction that results in a
successful transaction (transmission/reception) with the SAP.
[0102] The previous aspect of the invention was explained in
reference to a single STA communicating with the SAP. When multiple
stations contend to access the C-CBP, collisions occur. Therefore,
there is a need for a back-off procedure that accounts for the
directivity of the stations.
[0103] According to one aspect of the invention, an STA uses a set
of N random back-off numbers R(1), R(2), . . . , R(N) for
determining the number of back-off time slots (or equivalently,
time cycles and time slots within the time cycles) before
transmission corresponding to the N SAP receive directions. The
n.sup.th random number R(n) indicates the number of back-off time
slots for a given target SAP receive direction number (i.e., when
the SAP employs its receive direction number n). Therefore, the
candidate time slots to be considered for back-off random number
R(n) are the time slots where the SAP's receive direction is
denoted by direction number n. For example, in reference to the
numbering scheme in FIG. 6B, these candidate time slots include
time-slots number n+k.times.N for any k (that is candidate time
slots are time-slot numbers n+N, n+2.times.N, n+3.times.N, etc.).
The random number R(n) determines the time-cycle number, and n
determines the time-slot number within the selected time cycle.
According to another aspect of the invention, a set of N binary
exponential back-off window sizes W(1), W(2), . . . , W(N)
corresponding to the set of N SAP receive directions may be used.
The back-off window sizes are initially set to some initial values
2.sub.A(1), 2.sub.A(2), . . . , 2.sub.A(N). That is,
W(1)=2.sub.A(1), W(2)=2.sub.A(2), . . . ,W(N)=2.sub.A(N). The
initial values A(1), A(2), . . . , A(N) may be equal or they may be
different.
[0104] According to one aspect of the invention, an STA that needs
to transmit in the C-CBP draws a set of N random numbers R(1),
R(2), . . . , R(N), where R(n) is between 1 and W(n) for n=1, 2, .
. . , N. As explained above, the random number R(n) determines the
number of back-off time cycles, and the target time slot is the
n.sup.th time slot in cycle number R(n). According to one aspect of
the invention, the STA sorts the set of random numbers in ascending
order R[t(1)].ltoreq.R[t(2)].ltoreq. . . . .ltoreq.R[t(N)], where
t(1) is the index of the smallest random number, t(2) is the index
of the second smallest random number and so on. The first request
frame is transmitted using transmit direction number t(1) in the
t(1).sup.th time-slot number in cycle number R[t(1)]; that is, in
time-slot number {R[t(1)]-1}.times.N+t(1) if the time slots are
numbered 1, 2, 3, . . . from the boundary of the C-CBP, such as
shown in FIG. 6B. If the transaction is not unsuccessful, the STA
transmits a second request frame using transmit direction number
t(2) in the t(2).sup.th time slot in cycle number R[t(2)]; that is,
in time-slot number [t(2)-1].times.N+1; and so on. If R[t(n)] for
some n is bigger than the number of slots available in the C-CBP,
the transmission is delayed until the next C-CBP in the next
superframe. Each time a transaction is unsuccessful, the
corresponding back-off window size is increased. According to one
aspect of the invention, the back-off window size is doubled every
time the transaction is unsuccessful in a given SAP receive
direction until it reaches a maximum predetermined value, after
which, it is kept unchanged until the transaction is successful or
the STA ceases its attempts. For example, after the transmission of
the first request frame in transmit direction number t(1) in the
t(1).sup.th time slot in cycle number R[t(1)], if the transaction
was unsuccessful, the STA doubles the value of the back-off window
size W[t(1)]. So if all of the first N trials are unsuccessful, the
next set of N random numbers R(1), R(2), . . . , R(N) are drawn
from 1 and 2*W(n) for n=1, 2, . . . N, and so on.
[0105] Aspects of the invention are further described with
reference to FIG. 8. In this example, the SAP is assumed to have
three receive directions (i.e., N=3), and the C-CBP 802 is divided
into 24 time slots 806 to 860 corresponding to 8 cycles 804-1 to
804-8, where each cycle 804-1 to 804-8 contains three time slots
corresponding to the three SAP receive directions. As before, the
SAP changes receive direction from one time slot to another. For
example, the SAP uses receive direction number 1 in time-slot
number 1, receive direction number 2 in time-slot number 2, receive
direction number 3 in time-slot number 3, receive direction number
1 in time-slot number 4, receive direction number 2 in time slot
number 5, receive direction number 3 in time-slot number 6, and so
on. The above aspect of the invention is explained with exemplary
initial back-off window sizes W(1)=W(2)=W(3)=8. The STA draws three
random numbers, R(1), R(2) and R(3). In the case depicted in FIG.
8, these random numbers are R(1)=5, R(2)=3, and R(3)=6. The STA
sorts these three numbers, as explained previously. In this
example, t(1)=2, t(2)=1, and t(3)=3. The STA sends a first request
frame using transmit direction number 2 (since t(1)=2) in the
2.sup.nd time slot in cycle number 3 (since R[t(1)]=R(2)=3), that
is, in time slot 820, which is time slot number 8 (since
{R[t(1)]-1}.times.N+t(1)={R(2)-1}.times.3+2=8). If the transaction
is unsuccessful, the STA transmits a second request frame using
transmit direction number 1 (since t(2)=1) in the 1.sup.st time
slot in cycle number 5 (since R[t(2)]=R(1)=5), that is, in time
slot 830, which is time-slot number 13 (since
{R[t(2)]-1}.times.N+t(2)={R(1)-1}.times.3+1=8). If the second
transaction is unsuccessful, the STA transmits a third request
frame using transmit direction number 3 (since t(3)=3) in the
3.sup.rd time slot in cycle number 6 (since R[t(3)]=R(3)=6), that
is, in time slot 840, which is time-slot number 18 (since
{R[t(3)]-1}.times.N+t(3)={R(3)-1}.times.3+3=18).
[0106] According to one aspect of the invention, upon a successful
transaction, the STA uses the pair of working directions in which
the successful transaction occurred for future communication with
the SAP. If, for example, the third transaction was successful,
then according to another aspect of the invention, the STA contends
only in slots number 3*n for n=1, 2, 3, . . . . That is, if the STA
needs to send a request frame in the next superframe, the only
candidate slots for possible transmissions are time-slots number 3,
6, 9, 12, 15, 18, 21, and 24. The STA uses a single back-off window
size W=W(3) and a single random number R=R(3) to access the C-CBP.
Furthermore, the STA uses the same transmit direction it used
during the successful transaction. In summary, upon a successful
transaction, the STA has knowledge of the following: a) A working
transmit direction toward the SAP, referred to as STA transmit
direction number p; b) an SAP working receive direction, referred
to as the SAP receiver direction number n; c) the STA's preferred
receive direction from the SAP, referred to as the STA receive
direction number q; and d) the SAP's preferred transmit direction
to the STA, referred to as the SAP transmit direction number m. The
STA uses this pair of downlink and uplink directions for further
communication with the SAP.
[0107] According to one aspect of the invention, after a successful
transaction with an STA, such as described above, the SAP stores a
preferred transmit direction to the STA and, optionally, a working
receive direction from the STA. Furthermore, the STA stores a
preferred receive direction from the SAP and a working transmit
direction toward the SAP.
[0108] According to one aspect of the invention, the STA may use
the C-CBP to find a preferred downlink using the directional
back-off procedure described above. Upon a successful transaction
with the SAP, the SAP has a working downlink pair of directions
(i.e., the STA working transmit direction number p and the SAP
working receive direction number n). This pair of working downlink
directions is not necessarily the best pair of directions. The SAP
has N receive directions and the STA has P transmit directions. In
some aspects of the invention, the SAP surveys all direction
combinations (i.e., N.times.P directions) and the SAP measures the
LQI for each combination (nc,pc), where nc=1 to N and pc=1 to P, to
find a preferred pair of downlink directions. Upon a first
successful transaction, the STA will have tried the following
combinations: a) N transactions in N times-slots in which the STA
uses direction number 1 and the SAP cycles through its N directions
one at a time per time slot; b) N transactions in N times-slots in
which the STA uses direction number 2 and the SAP cycles through
its N directions one at a time per time slot; c) p-1 transactions
in N times-slots in which the STA uses direction number p-1 and the
SAP cycles through its N directions one at a time per time slot;
and d) n time slots in which the STA uses direction number p and
the SAP cycles through directions 1 to n, where in the last time
slot, the working pair of directions (the STA transmit direction
number p and the SAP receive direction number m) were found.
Therefore, the STA has gone through N.times.(p-1)+n transactions
where only the last one was successful. The STA may choose to
continue the procedure, that is, the remaining
N.times.P-[N.times.(p-1).times.n] combinations of directions, using
the above directional exponential back-off procedure in order to
find a preferred downlink pair with a preferred LQI. If the STA
completes its trial of all N.times.P directions, this is a full
double sweep. Otherwise, if the STA stops at the first working
downlink pair of directions, it is a partial successful double
sweep.
[0109] According to one aspect of the invention, if an STA performs
a full double sweep, the SAP measures the LQI for each successful
reception of a request frame and sends the LQI as a feedback in one
of the fields of the response frame. Furthermore, the STA may sort
LQIs (either all LQIs or just those above a given threshold) and
select at least one preferred downlink pair for further
transactions with the SAP. The preferred uplink pair is obtained
from the beacon frames, as explained above, and may not be part of
the C-CBP direction search.
[0110] According to one aspect of the invention, if an STA performs
a full double sweep, the SAP measures the LQI for each successful
reception of a request frame and sends the LQI as a feedback in one
of the fields of the response frame. Furthermore, the SAP may sort
LQIs (either all LQIs or just those above a given threshold) and
then provide feedback to the STA. The STA may select the preferred
downlink pair for further transactions with the SAP. The preferred
uplink pair is obtained from the beacon frames, as explained above,
and may not be part of the C-CBP direction search.
[0111] According to one aspect of the invention, upon finding a
working or preferred pair of uplink and downlink directions (the
SAP's transmit direction number, m, the SAP's receive direction
number, n, the STA's transmit direction number, p, and the STA's
receive direction number, q) an STA having a request frame to send
may use a single back-off window size, W, and a single uniform
number generator. According to one aspect of the invention, the STA
generates a uniform random number R in the range 1 to W and uses
the n.sup.th time slot in time-cycle number Z to transmit the
request frame using transmit direction number p. If this is the
first attempt by the STA to transmit the request frame, then Z=R.
if this is not the first attempt by the STA to transmit the request
frame, then Z=R+RACC, where RACC is the number of the time cycle
used during the last unsuccessful transmission of the request
frame. This procedure is part of the directional slotted ALOHA
protocol and is used after the STA has knowledge of at least the
working or preferred transmit direction to the SAP.
[0112] In the case in which an STA is moving, the preferred or
working pair of downlink directions may change.
[0113] According to another aspect of the invention, after a full
or partial successful double sweep, an STA keeps a list of K
downlink direction pairs (for example, a best pair and a
second-best pair) and tracks and update the list by using the
directional back-off algorithm in the appropriate time slots. In
one aspect of the invention, 2 pairs are maintained; a best pair
(p.sub.1,n.sub.1) of downlink directions and a second-best pair
(p.sub.2,n.sub.2), where the first index (p.sub.1 or p.sub.2)
refers to the STA transmit direction number and the second index
(n.sub.1 or n.sub.2) refers to the SAP receive direction number.
The STA may determine the LQI of its best transmit direction
(measured by the SAP and sent back to the STA in the response
frame) in every superframe and determine the LQI of the second best
transmit direction (measured by the SAP and sent back to the STA in
the response frame) during every other superframe. So according to
another aspect of the invention, the tracking of the downlink
direction pairs occurs at different update rates. When the STA
updates the LQI of the best downlink direction pair
(p.sub.1,n.sub.1), it may use the directional exponential back-off
algorithm. For example, the STA uses a back-off window size W1 and
draws a random number R.sub.1(1), where R.sub.1(1) is between 1 and
W1. The STA sends a request frame in the n.sub.1.sup.th slot of
cycle number R.sub.1 (i.e., in slot number
[R.sub.1(1)-1].times.N+n.sub.1). The request frame contains
information about the SAP's preferred transmit direction n1 from
the STA's perspective, information that is available to the STA as
a result of decoding and tracking the beacon frames. The SAP
receives the request frame using direction number n1, measures the
LQI of the request, and send the LQI back to the STA in the
response frame. The SAP transmits the response frame using transmit
direction number n1, and the STA receives the response using
receive direction number q. Furthermore, the STA may update its
list after each feedback or at the end of the double sweep. The
request packet and response packet may be sounding packets, which
are specialized packets used for measuring and reporting channel
conditions and LQI. If the STA does not receive the response
packet, or the response packet was not correctly decoded, the STA
doubles the back-off window size W1, draws a random number
R.sub.1(2), and a second attempt is initiated by sending a request
frame in the n.sub.1.sup.th time slot of cycle number
[R.sub.1(1)+R.sub.1(2)], that is, in slot number
[R.sub.1(1)+R.sub.1(2)-1].times.N+n.sub.1. The STA waits for a
response, and if the response packet is decoded correctly, the STA
receives the LQI (which was sent in the response frame by the SAP)
and updates its list of K downlink direction pairs. Each item of
the list may simply contain the pair of directions (p,n) or the
index p, and the corresponding LQI measured by the SAP. In the
event of a predetermined number of unsuccessful transactions for
the pair (p1,n1), the STA may remove the pair (p1,n1) from the list
and select (p2,n2) as an alternative or temporary preferred pair
until a better pair is found.
[0114] According to one aspect of the invention, if during or after
updating the STA's list of K downlink direction pairs, a better
downlink direction pair is discovered, the STA may select the
better downlink direction pair for further transactions with the
SAP.
[0115] According to one aspect of the invention, the C-CBP is used
for at least one of STA authentication, association, transmit
and/or receive direction finding, direction tracking, control
frames, service period reservation, command frames, management
frames, and data frames, where in all cases, the communication is
between the STA and the SAP. An STA may use the directional
slotted-ALOHA protocol in the C-CBP to exchange data frames with
the SAP. However, the length of the data frames should be selected
such that a transaction does not exceed the slot boundary. If the
frame is too long, it should be adapted to fit within a time slot
along with the response and two SIFS. As another example of a data
transaction, the request frame may be a data frame and the response
frame may be an immediate acknowledgment. For association, the
request frame may be an association request and the response frame
may be an association response. Peer-to-peer communications in
which neither peer is an SAP is preferably performed in the D-CBP.
As another example, the request frame can be a service period
reservation request by an STA, and the response frame sent by the
SAP may be the SAP denial or acceptance of the service period
reservation. Each task (such as association, authentication,
service period reservation, etc.) may require more than a simple
exchange of two frames (i.e., the request frame and response
frame). Rather, a task may require multiple request-response
frames. Direction finding may be performed using a full double
sweep or a partial successful double sweep. The direction
acquisition (finding) can be performed as part of authentication
and/or association, or it may be performed independently. When
performed independently, it is preferably done before any other
task in the C-CBP, such as before authentication, association, and
data exchange. If the direction acquisition is accomplished as an
independent STA task, the request and response frames used during
the sweep may be specialized sounding packets. Alternatively, if
the direction acquisition is part of authentication, then the
request and response frames are authentication request and response
frames.
[0116] According to another aspect of the invention, a directional
cycle-based ALOHA method is employed wherein the directional
exponential back-off is cycle-based rather than slot-based.
Specifically, an STA may use a single back-off window size W and a
single random number R. The STA generates a random number R.sub.1
(1.ltoreq.R.sub.1.ltoreq.W) that is used for the first N candidate
transmissions in N time slots in cycle number R. The STA transmits
a first request frame using transmit direction number 1 in the
first time slot of time-cycle number R. During the first time slot,
the SAP employs its first receive direction. If the STA does not
receive a response, the transaction is unsuccessful, so the STA
transmits a second request frame in transmit direction number 1 in
the second time slot of time-cycle number R. The SAP employs its
second receive direction in the second time slot, and the STA
listens for a response. This process may be repeated for all N time
slots within the time-cycle number R. If there are no successful
transactions, the STA doubles its back-off window and generates a
second random number R.sub.2 (1.ltoreq.R.sub.2.ltoreq.2W). The
random number R.sub.2 is used for the second set of N scheduled
transmissions in N time slots in cycle number R.sub.1+R.sub.2, and
the STA repeats its transmission process using transmit direction
number 2. This process may be repeated for all the STA transmit
directions.
[0117] An STA may use both directional cycle-based ALOHA and
directional slot-based ALOHA. As an example, an STA may use
cycle-based ALOHA for initial direction acquisition (e.g.,
direction-finding) during a partial or full double sweep. In this
case, an STA may finish the double sweep in P (non-consecutive)
cycles such that within each time cycle, the STA employs a fixed
transmit direction and the SAP sweeps over all of its receive
directions, one receive direction per time slot. When a preferred
downlink pair of directions is found, the pair may be used for
authentication, association, and further data transfer with a
directional slotted ALOHA protocol, as previously described.
[0118] FIG. 9A illustrates an exemplary method 900 for encoding the
centralized contention based period (C-CBP) in a beacon frame. A
beacon is generated by an SAP 902, and the C-CBP information and
the superframe timing and structure are encoded in the beacon 904
before transmission 906.
[0119] FIG. 9C illustrates an exemplary method 940 that may be
performed by an STA to process a received beacon frame. An STA
receives a beacon frame 942, demodulates the beacon frame 944, and
extracts C-CBP and superframe information 946.
[0120] FIG. 10A illustrates an exemplary method 1000 for processing
a frame for transmission by an STA using a directional slotted
ALOHA protocol. An STA prepares a data frame for transmission 1002.
The STA generates a set of N uniform random variables R(1) to R(N)
1004, where N is the number of SAP receive directions and R(n) is
in the range of 1 to W(n), where W(n) is the n.sup.th back-off
window size and n=1 to N. The STA sorts the list of random numbers
in increasing order 1006. For example, the sorted list may be
expressed by R[T(1)].ltoreq.R[T(2).ltoreq. . . . .ltoreq.R[T(N)].
The STA transmits the frame 1008 in the T(NC).sup.th time slot of
cycle number R[T(NC)] for at least some NC=1 to N. FIG. 10B
illustrates an apparatus configured for performing the steps shown
in FIG. 10A.
[0121] FIG. 10C illustrates an exemplary method 1040 for processing
a request frame by an SAP using a directional slotted ALOHA
protocol. An SAP receives a request frame 1042. The SAP detects and
decodes the request frame 1044 to extract information encoded in
the frame regarding the transmit direction (e.g., a transmit
direction index) it should use for sending response frames to the
STA. The SAP stores the STA ID and the transmit direction index
1046. FIG. 10D illustrates an apparatus configured for performing
the steps shown in FIG. 10C.
[0122] FIG. 11A illustrates an exemplary method 1100 for frame
transmission by an STA using a directional slotted ALOHA protocol
wherein the STA has knowledge of the working direction toward the
SAP. The STA prepares a frame for retransmission 1102. The STA
obtains information 1104 (such as from a previous partial or full
double sweep) regarding its transmit direction number (PC), SAP
receive direction number (NC), SAP transmit direction number (MC),
the back-off window size W, and cycle number (RAcc) where the last
transmission from the STA toward the SAP with the SAP in receive
direction number (NC) has occurred. The STA encodes the SAP's
transmit direction (MC) in the request frame 1106 in order to
inform the SAP that this is the direction to use to transmit the
response frame. The STA generates a uniform random number 1108 in
the range 1 to W. The STA transmits the request frame 1110 using
transmit direction number (PC) in the NC.sup.th time slot of
time-cycle number R+RACC. FIG. 11B illustrates an apparatus
configured for performing the steps shown in FIG. 11A.
[0123] FIG. 12A illustrates an exemplary method 1200 according to
one aspect of the invention. An SAP receives a request frame from
an STA 1202 wherein the STA has encoded the transmit direction NC
that the SAP should use for transmitting frames to the STA. The SAP
decodes the request frame 1204 to obtain the transmit direction NC
it should use for responding back to the STA. The SAP generates a
response frame 1206 and transmits the response frame 1208 using
transmit direction number NC. FIG. 12B illustrates an apparatus
configured for performing the steps shown in FIG. 12A.
[0124] FIG. 13A illustrates an exemplary method 1300 performed by
an STA to find at least one working or preferred downlink
direction. The STA performs a full or partial double sweep using
the directional slotted ALOHA protocol 1302. The STA determines
preferred or working downlink directions from response frames
received from the SAP 1304. The STA transmits the preferable or
working downlink directions 1306 to the SAP. FIG. 13B illustrates
an apparatus configured for performing the steps shown in FIG.
13A.
[0125] The various operations of methods described above may be
performed by any suitable means capable of performing the
corresponding functions. The means may include various hardware
and/or software component(s) and/or module(s), including, but not
limited to a circuit, an application specific integrated circuit
(ASIC), or processor. Generally, where there are operations
illustrated in Figures, those operations may have corresponding
counterpart means-plus-function components with similar numbering.
For example, blocks 902-906, 942-946, 1002-1008, 1042-1046,
1102-1110 1202-1208, and 1302-1306, illustrated in FIGS. 9A, 9C,
10A, 10C, 11A, 12A and 13A correspond to circuit blocks 922-926,
962-966, 1022-1028, 1062-1066, 1122-1130, 1222-1228 and 1322-1326
illustrated in FIGS. 9B, 9D, 10B, 10D, 11B, 12B and 13B.
[0126] As used herein, the term "determining" encompasses a wide
variety of actions. For example, "determining" may include
calculating, computing, processing, deriving, investigating,
looking up (e.g., looking up in a table, a database or another data
structure), ascertaining and the like. Also, "determining" may
include receiving (e.g., receiving information), accessing (e.g.,
accessing data in a memory) and the like. Also, "determining" may
include resolving, selecting, choosing, establishing and the
like.
[0127] The various operations of methods described above may be
performed by any suitable means capable of performing the
operations, such as various hardware and/or software component(s),
circuits, and/or module(s). Generally, any operations illustrated
in the Figures may be performed by corresponding functional means
capable of performing the operations.
[0128] The various illustrative logical blocks, modules and
circuits described in connection with the present disclosure may be
implemented or performed with a general purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array signal (FPGA) or
other programmable logic device (PLD), discrete gate or transistor
logic, discrete hardware components or any combination thereof
designed to perform the functions described herein. A general
purpose processor may be a microprocessor, but in the alternative,
the processor may be any commercially available processor,
controller, microcontroller or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0129] The steps of a method or algorithm described in connection
with the present disclosure may be embodied directly in hardware,
in a software module executed by a processor, or in a combination
of the two. A software module may reside in any form of storage
medium that is known in the art. Some examples of storage media
that may be used include random access memory (RAM), read only
memory (ROM), flash memory, EPROM memory, EEPROM memory, registers,
a hard disk, a removable disk, a CDROM and so forth. A software
module may comprise a single instruction, or many instructions, and
may be distributed over several different code segments, among
different programs, and across multiple storage media. A storage
medium may be coupled to a processor such that the processor can
read information from, and write information to, the storage
medium. In the alternative, the storage medium may be integral to
the processor.
[0130] The methods disclosed herein comprise one or more steps or
actions for achieving the described method. The method steps and/or
actions may be interchanged with one another without departing from
the scope of the claims. In other words, unless a specific order of
steps or actions is specified, the order and/or use of specific
steps and/or actions may be modified without departing from the
scope of the claims.
[0131] The functions described may be implemented in hardware,
software, firmware or any combination thereof. If implemented in
software, the functions may be stored as one or more instructions
on a computer-readable medium. A storage media may be any available
media that can be accessed by a computer. By way of example, and
not limitation, such computer-readable media can comprise RAM, ROM,
EEPROM, CD-ROM or other optical disk storage, magnetic disk storage
or other magnetic storage devices, or any other medium that can be
used to carry or store desired program code in the form of
instructions or data structures and that can be accessed by a
computer. Disk and disc, as used herein, include compact disc (CD),
laser disc, optical disc, digital versatile disc (DVD), floppy
disk, and Blu-ray.RTM. disc where disks usually reproduce data
magnetically, while discs reproduce data optically with lasers.
[0132] Thus, certain aspects may comprise a computer program
product for performing the operations presented herein. For
example, such a computer program product may comprise a computer
readable medium having instructions stored (and/or encoded)
thereon, the instructions being executable by one or more
processors to perform the operations described herein. For certain
aspects, the computer program product may include packaging
material.
[0133] Software or instructions may also be transmitted over a
transmission medium. For example, if the software is transmitted
from a website, server, or other remote source using a coaxial
cable, fiber optic cable, twisted pair, digital subscriber line
(DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of transmission
medium.
[0134] Further, it should be appreciated that modules and/or other
appropriate means for performing the methods and techniques
described herein can be downloaded and/or otherwise obtained by a
user terminal and/or base station as applicable. For example, such
a device can be coupled to a server to facilitate the transfer of
means for performing the methods described herein. Alternatively,
various methods described herein can be provided via storage means
(e.g., RAM, ROM, a physical storage medium such as a compact disc
(CD) or floppy disk, etc.), such that a user terminal and/or base
station can obtain the various methods upon coupling or providing
the storage means to the device. Moreover, any other suitable
technique for providing the methods and techniques described herein
to a device can be utilized.
[0135] It is to be understood that the claims are not limited to
the precise configuration and components illustrated above. Various
modifications, changes and variations may be made in the
arrangement, operation and details of the methods and apparatus
described above without departing from the scope of the claims.
[0136] The techniques provided herein may be utilized in a variety
of applications. For certain aspects, the techniques presented
herein may be incorporated in a base station, a mobile handset, a
personal digital assistant (PDA) or other type of wireless device
that operate in UWB part of spectrum with processing logic and
elements to perform the techniques provided herein.
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