U.S. patent application number 10/551941 was filed with the patent office on 2007-01-11 for method and system for retransmission.
Invention is credited to Johan Torsner.
Application Number | 20070008990 10/551941 |
Document ID | / |
Family ID | 33157496 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070008990 |
Kind Code |
A1 |
Torsner; Johan |
January 11, 2007 |
Method and system for retransmission
Abstract
The present invention relates to retransmissions in a
communications system. A method and system of reducing uplink
retransmission delay of a radio communications system by
introducing an uplink MAC ARQ layer of Node B is disclosed.
Further, a MAC PDU data indicator for soft combining control in
Node B and RLC PDU reordering is introduced.
Inventors: |
Torsner; Johan; (FInland,
SE) |
Correspondence
Address: |
ERICSSON INC.
6300 LEGACY DRIVE
M/S EVR C11
PLANO
TX
75024
US
|
Family ID: |
33157496 |
Appl. No.: |
10/551941 |
Filed: |
April 10, 2003 |
PCT Filed: |
April 10, 2003 |
PCT NO: |
PCT/SE03/00589 |
371 Date: |
September 14, 2006 |
Current U.S.
Class: |
370/473 |
Current CPC
Class: |
H04L 1/1841 20130101;
H04L 1/1835 20130101; H04L 1/18 20130101; H04L 1/1809 20130101;
H04L 1/1845 20130101 |
Class at
Publication: |
370/473 |
International
Class: |
H04J 3/24 20060101
H04J003/24 |
Claims
1. A method of reducing impact of transmission errors by means of a
retransmission protocol, utilizing a retransmission loop involving
packet radio transmissions from user equipment to a control element
connected to one or more radio base stations, wherein the user
equipment radio transmissions are received at one or more radio
base stations for forwarding to the control element, the base
station acknowledging, positively or negatively, transmissions from
the user equipment and the control element acknowledging,
positively or negatively, transmissions forwarded to it.
2. The method according to claim 1, wherein for a process of
retransmission, if same transmitted packet information content is
received more than once, the received transmissions are
combined.
3. The method according to claim 2, wherein successive received
packet transmissions of the same information content are combined
in the base station prior to determining whether or not the radio
base station should acknowledge the transmitted information
content.
4. The method according to claim 2, wherein whether or not the
packet information content is the same is determined by means of a
new data indicator.
5. The method according to claim 4, wherein the new data indicator,
accompanying packet information, is transmitted on a reliable
control channel.
6. The method according to claim 2, wherein the process is
identified by means of a process identity.
7. The method according to claim 6, wherein the process identity,
accompanying packet information, is transmitted on a reliable
control channel.
8. The method according to claim 1, wherein the control element
reorders received packets.
9. The method according to claim 8, wherein the received packets
are reordered into sequential order.
10. The method according to claim 9, wherein the sequential order
is determined from RLC sequence number.
11. The method according to claim 9, wherein the sequential order
is determined from MAC sequence number.
12. The method according to claim 1, wherein the method reduces
delay of uplink transmissions, the delay being associated with the
retransmissions.
13. A signal format for uplink transmissions from user equipment to
radio base station of a radio communications system, wherein the
signal format comprises signal elements allowing radio base station
reception combining and acknowledgment of successive received
transmissions concerning same data in uplink direction prior to
forwarding received transmissions, the signal elements comprising:
process identity, new data indicator, and payload, wherein the new
data indicator indicates whether or not payload data of a process
with identity as indicated by the process identity element has been
transmitted previously.
14. The signal format according to claim 13, wherein the process
identity and new data indicator elements are more strongly
protected by a forward error control code than payload.
15. The signal format according to claim 13, wherein the process
identity and new data indicator elements are transmitted on a
control channel in synchronism with transmissions of the payload
element.
16. The signal format according to claim 15, wherein the control
channel is a shared control channel of a UMTS or WCDMA system.
17. The signal format according to claim 15, wherein the control
channel is a dedicated control channel of a UMTS or WCDMA
system.
18. The signal format according to claim 13, wherein the payload
element comprising an integer number of radio link control protocol
data units (RLC PDUs).
19. The signal format according to claim 13, wherein the process
identity, new data indicator and payload elements are arranged for
uplink transmission in a transmission time interval shorter than 10
milliseconds.
20. The signal format according to clam 19, wherein the process
identity, new data indicator and payload elements are arranged for
uplink transmission in a transmission time interval shorter than 4
milliseconds.
21. A radio network controller of a radio communications system,
comprising: receive means for receiving one or more transmissions
originated in a UE in uplink direction from one or more radio base
stations where the one or more transmissions in uplink direction
have been pre-detected according to an ARQ protocol, receive means,
for receiving first protocol data units, buffering means, for
buffering received first protocol data units, segmentation means,
for segmenting received first protocol data units into second
protocol data units, reassemble means, for reassembling second
protocol data units into service data units, transfer means, for
transferring service data units, and reordering means, for
reordering first or second protocol data units.
22. The radio network controller according to claim 21, further
comprising: processing means, and transmit means, the processing
means being arranged to verify second protocol data units according
to an error detecting code and the transmit means transmitting
positive or negative acknowledgments depending on whether or not
the second protocol data unit is detected to be erroneous.
23. The radio network controller according to claim 21, wherein the
reordering means rearranges the second protocol data units
according to an RLC sequence number.
24. The radio network controller according to claim 21, further
comprising receive means arranged for receiving first protocol data
units concerning a particular connection from a plurality of first
protocol data senders.
25. The radio network controller according to claim 21, wherein the
first protocol data units are MAC PDUs.
26. The radio network controller according to claim 21, wherein the
second protocol data units are RLC PDUs.
27. The radio network controller according to claim 21, wherein the
radio network controller is a radio network controller of a UMTS or
WCDMA system.
28. A radio base station, comprising: receive means, for receiving
one or more first protocol data units, a protocol entity, for
processing first protocol data units, and transmit means, for
transmitting acknowledgments and for forwarding of first protocol
data units.
29. The radio base station according to claim 28, further
comprising: buffering means, for buffering one or more first
protocol data units.
30. The radio base station according to claim 28, wherein the
protocol entity is arranged for verifying one or more first
protocol data units according to a forward error control code, and
depending on the outcome positively or negatively acknowledging to
an uplink transmitting entity received first one or more protocol
data units.
31. The radio base station according to claim 28, further
comprising means for combining received first protocol data units,
the protocol entity being arranged to verify the combined protocol
data unit according to a forward error control code and depending
on the outcome positively or negatively acknowledging to an uplink
transmitting entity the latest received protocol data unit of the
combination.
32. The radio base station according to claim 31, wherein the first
protocol data units with same process identity are combined
according to a received new data indicator.
33. The radio base station according to claim 28, wherein the first
protocol data units are MAC PDUs.
34. The radio base station according to claim 28, wherein the radio
base station is a radio base station of a UMTS or WCDMA system.
35. A user equipment apparatus of a radio communications system,
comprising: assemble means for assembling one or more second
protocol data units into one or more first protocol data units,
buffering means for buffering first protocol data units, transmit
means for transmitting first protocol data units according to an
ARQ protocol, receive means for receiving one or more
acknowledgments of first protocol data units, and receive means for
receiving one or more acknowledgments of second protocol data
units.
36. The user equipment apparatus according to claim 35, wherein the
transmit means is arranged to retransmit one or more first protocol
data units if negatively acknowledged or not positively
acknowledged within a predetermined time.
37. The user equipment apparatus according to claim 35, further
comprising buffering means arranged to release buffer space of one
or more first protocol data units if positively acknowledged or not
negatively acknowledged within a predetermined time.
38. The user equipment apparatus according to claim 35, further
comprising transmit means being arranged to transmit first protocol
data units in transmission time intervals shorter than 10
milliseconds.
39. The user equipment apparatus according to claim 38, further
comprising transmit means arranged to transmit first protocol data
units in transmission time intervals shorter than 4
milliseconds.
40. The user equipment according to claim 35, wherein the first
protocol data units are MAC PDUs.
41. The user equipment according to claim 35, wherein the second
protocol data units are RLC PDUs.
42. The user equipment apparatus according to claim 35, wherein the
user equipment apparatus is user equipment of a UMTS or WCDMA
system.
43-46. (canceled)
47-48. (canceled)
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to retransmissions in a
communications system, and more especially it relates to a cellular
mobile radio system, particularly to a Universal Mobile
Telecommunications System, UMTS or WCDMA system.
BACKGROUND AND DESCRIPTION OF RELATED ART
[0002] Retransmission of data to or from a mobile station, MS, or
user equipment, UE, is previously known. It is also known to use
medium access control and radio link control layers of a UMTS
protocol structure in acknowledged mode for dedicated channels.
[0003] In acknowledged mode, retransmissions are undertaken in case
of detected transmission errors not recovered by forward error
control. This is also called automatic repeat request, ARQ. With
ARQ, retransmissions can be undertaken unless a transmitted message
is (positively) acknowledged. Retransmissions could also be
initiated at explicit negative acknowledgments of transmitted
messages. Generally there are time limits for the respective
positive and negative acknowledgements to be considered.
[0004] Within this patent application, a radio network controller,
RNC, is understood as a network element including a radio resource
controller. Node B is a logical node responsible for radio
transmission/reception in one or more cells to/from a User
Equipment. A base station, BS, is a physical entity representing
Node B.
[0005] Medium access control, MAC, and radio link control, RLC, is
used within radio communications systems like General Packet Radio
Services, GPRS, and UMTS.
[0006] U.S. Pat. No. 5,570,367 discloses a wireless communications
system arranged to transmit acknowledgement and request for
retransmission messages. Data received in a microcell from an end
user device is forwarded to a cell site. Data received by the cell
site is transmitted to a cellular switch. A base station sends a
poll message to the end user device, inquiring for the status of
unacknowledged messages previously transmitted from the base
station.
[0007] Also, a base station transmitter window is defined. A lower
end pointer identifies a lowest numbered packet transmitted to and
acknowledged by the base station. The upper end pointer identifies
the highest numbered packet transmitted by the base station.
Consequently, the window represents packets transmitted by the base
station and unacknowledged by the end user device.
[0008] International Patent Application WO02096044 reveals a method
and system of reducing or eliminating transmissions over a scarce
communication link resource in a communications system by
establishing an image of downlink transmissions status.
[0009] International Patent Application PCT/SE02/02186 includes a
method and system for in-sequence delivery of RLC PDUs, transmitted
in downlink direction, to a user equipment at handover.
[0010] 3.sup.rd Generation Partnership Project (3GPP): Technical
Specification Group Radio Access Network, Physical Layer
Procedures, 3G TS 25.301 v3.6.0, France, September 2000, specifies
in chapter 5 Radio Interface Protocol Architecture of a UMTS
system. There are three protocol layers: [0011] physical layer,
layer 1 or L1, [0012] data link layer, layer 2 or L2, and [0013]
network layer, layer 3 or L3.
[0014] Layer 2, L2, and layer 3, L3 are divided into Control and
User Planes. Layer 2 consists of two sub-layers, RLC and MAC, for
the Control Plane and four sub-layers, BMC, PDCP, RLC and MAC, for
the User Plane. The acronyms BMC, PDCP, RLC and MAC denote
Broadcast/Multicast Control, Packet Data Convergence Protocol,
Radio Link Control and Medium Access Control respectively.
[0015] FIG. 1 illustrates a simplified UMTS layers 1 and 2 protocol
structure for a Uu Stratum, UuS, or Radio Stratum, between a user
equipment UE and a Universal Terrestrial Radio Access Network,
UTRAN.
[0016] Radio Access Bearers, RABs, make available radio resources
(and services) to user applications. For each mobile station there
may be one or several RABs. Data flows (in the form of segments)
from the RABs are passed to respective Radio Link Control, RLC,
entities which amongst other tasks buffer the received data
segments. There is one RLC entity for each RAB. In the RLC layer,
RABs are mapped onto respective logical channels. A Medium Access
Control, MAC, entity receives data transmitted in the logical
channels and further maps logical channels onto a set of transport
channels. In accordance with subsection 5.3.1.2 of the 3GPP
technical specification MAC should support service multiplexing
e.g. for RLC services to be mapped on the same transport channel.
In this case identification of multiplexing is contained in the MAC
protocol control information.
[0017] Transport channels are finally mapped to a single physical
channel which has a total bandwidth allocated to it by the network.
In frequency division duplex mode, a physical channel is defined by
code, frequency and, in the uplink, relative phase (I/Q). In time
division duplex mode a physical channel is defined by code,
frequency, and time-slot. The DSCH (Downlink Shared Channel), e.g.,
is mapped onto one or several physical channels such that a
specified part of the downlink resources is employed. As further
described in subsection 5.2.2 of the 3GPP technical specification
the L1 layer is responsible for error detection on transport
channels and indication to higher layer, FEC encoding/decoding and
interleaving/deinterleaving of transport channels.
[0018] PDCP provides mapping between Network PDUs (Protocol Data
Units) of a network protocol, e.g. the Internet protocol, to an RLC
entity. PDCP compresses and decompresses redundant Network PDU
control information (header compression and decompression).
[0019] For transmissions on point-to-multipoint logical channels,
BMC stores at UTRAN-side Broadcast Messages received from an RNC,
calculates the required transmission rate and requests for the
appropriate channel resources. It receives scheduling information
from the RNC, and generates schedule messages. For transmission the
messages are mapped on a point-to-multipoint logical channel. At
the UE side, BMC evaluates the schedule messages and deliver
Broadcast Messages to upper layer in the UE.
[0020] 3G TS 25.301 also describes protocol termination, i.e. in
which node of the UTRAN the radio interface protocols are
terminated, or equivalently, where within UTRAN the respective
protocol services are accessible.
[0021] 3.sup.rd Generation Partnership Project (3GPP): Technical
Specification Group Radio Access Network, Physical Layer
Procedures, 3G TS 25.322 v3.5.0, France, December 2000, specifies
the RLC protocol. The RLC layer provides three services to the
higher layers: [0022] transparent data transfer service, [0023]
unacknowledged data transfer service, and [0024] acknowledged data
transfer service.
[0025] In subsection 4.2.1.3 an acknowledged mode entity,
AM-entity, is described (see FIG. 4.4 of the 3GPP Technical
Specification). In acknowledged mode automatic repeat request, ARQ,
is used. The RLC sub-layer provides ARQ functionality closely
coupled with the radio transmission technique used. The 3GPP
technical specification also reveals various triggers for a status
report to be transmitted. The receiver shall always send a status
report, if it receives a polling request. There are also three
status report triggers, which can be configured [0026] 1. Missing
PU(s) Detected, [0027] 2. Timer Initiated Status Report, and [0028]
3. Estimated PDU Counter.
[0029] For trigger 1, the receiver shall trigger transmission of a
status report to the sender if a payload unit, PU, is detected to
be missing. (One PU is included in one RLC PDU.) With trigger 2, a
receiver triggers transmission of a status report periodically
according to a timer. Finally, trigger 3 relates in short to a
timer corresponding to an estimated number of received PUs before
the requested PUs are received. The 3GPP Technical Specification
specifies a status PDU used to report the status between two RLC AM
(`Acknowledged Mode`) entities.
[0030] 3.sup.rd Generation Partnership Project (3GPP): Technical
Specification Group Radio Access Network, High Speed Downlink
Packet Access (HSDPA), Overall Description, 3G TS 25.308 v5.3.0,
France, December 2002, describes the overall support of High Speed
Downlink Packet Access in UTRA. FIGS. 5.1-1 and 5.1-2 illustrate
protocol architecture of HS-DSCH. Chapter 6 specifies HS-DSCH MAC
architecture for the downlink.
[0031] 3.sup.rd Generation Partnership Project (3GPP): Technical
Specification Group Radio Access Network, UTRAN Overall
Description, 3G TS 25.401 v4.5.0, France, September 2002, describes
the overall architecture of UTRAN, including internal interfaces
and assumptions on radio and Iu interfaces. Section 11.2.5 presents
the DSCH Transport channel. DSCH scheduling is performed by
MAC-c/sh in the CRNC.
[0032] 3.sup.rd Generation Partnership Project (3GPP): Technical
Specification Group Radio Access Network, Physical layer aspects of
UTRA High Speed Downlink Packet Access, 3G TS 25.848 v4.0.0,
France, March 2001, describes, among other things, physical layer
aspect of the techniques behind the concept of high-speed downlink
packet access (HSDPA). Section 6.3.1 presents a complexity analysis
of a dual channel stop-and-wait protocol for downlink hybrid
ARQ.
[0033] 3.sup.rd Generation Partnership Project (3GPP): Technical
Specification Group Radio Access Network, Physical layer aspects of
UTRA High Speed Downlink Packet Access, 3G TS 25.950 v4.0.0,
France, March 2001, describes several techniques for facilitating
high-speed downlink packet access. Chapter 8 describes various
properties of stop-and-wait hybrid ARQ.
[0034] None of the cited documents above discloses a method and
system of reducing uplink retransmission delay of a radio
communications system by introducing an uplink MAC ARQ layer of
Node B. Further, none of the cited documents mentions a MAC PDU
data indicator for soft combining control in Node B.
SUMMARY OF THE INVENTION
[0035] Cited prior art references describe retransmissions between
a UE and an RNC. According to preferred embodiments of the
invention, transmissions and retransmissions are partially
terminated in Node B, rendering soft combining of subsequent
transmissions possible. Corresponding acknowledgements (positive or
negative), if any, are terminated in UE.
[0036] Current WCDMA uplink connections has a latency in an
approximate range of 100-150 ms. This latency is of such an amount
that for some humans it is considered annoying, e.g., when using
interactive services over the connection.
[0037] Further, present WCDMA releases provide wide area coverage
for uplink data rates of 384 kbps. Applications proposed or
recently presented require high peak rates in the uplink.
[0038] Consequently, it is an object to reduce transmission delay
and latency over a scarce resource such as a radio interface.
[0039] A further object is to generate ARQ status reports in Node B
and to render possible soft combining of subsequent
(re-)transmissions.
[0040] It is also an object to segment RLC PDUs into MAC PDUs
suitable for transmission in one transmission time interval, that
may be shorter than allowed transmission time intervals of present
WCDMA releases.
[0041] Finally, it is an object to introduce a reordering entity of
RNC, handling RLC-PDUs received out of order, for improved
out-of-order handling at RNC.
[0042] These objects are met by the invention, which is
particularly well suited for a high-speed uplink packet access
channel of an evolved universal mobile telecommunications
system.
[0043] Preferred embodiments of the invention, by way of examples,
are described with reference to the accompanying drawings
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 displays a layered protocol structure, according to
prior art, in a radio communications system.
[0045] FIG. 2 displays a layered protocol structure, according to
the invention, in a radio communication system.
[0046] FIG. 3 shows communication, according to the invention,
between a UE and a base station involved in a connection between an
RNC and the UE.
[0047] FIG. 4 schematically illustrates MAC and RLC protocol
layers, according to the invention, in a multilayer protocol
structure.
[0048] FIG. 5 gives an overview of the uplink protocol structure
according to a preferred embodiment of the invention.
[0049] FIG. 6 shows a MAC PDU according to the preferred embodiment
of the invention.
[0050] FIG. 7 illustrates transmission of data and associated
control fields on separate channels, according to the
invention.
[0051] FIG. 8 illustrates N time multiplexed channels for N channel
stop-and-wait according to the preferred embodiment of the
invention.
[0052] FIG. 9 displays an RNC according to the invention.
[0053] FIG. 10 displays a Node B according to the invention.
[0054] FIG. 11 displays a User Equipment according to the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0055] FIG. 2 shows a preferred layered protocol structure, a
protocol stack, according to the invention. The L2 MAC layer of
FIG. 1 has been extended and divided into two sub-layers, a new L2
MAC sub-layer and a new MAC-ARQ sub-layer. Essentially the new L2
MAC sub-layer corresponds to the prior art L2 MAC sub-layer of FIG.
1. The MAC-ARQ plus the MAC layer could be regarded as one single
MAC layer extended to also include hybrid ARQ functionality.
However, for reasons of explanation they are preferably regarded as
separate sub-layers. Further, on the network side, considering them
as separate protocol sub-layers physically better corresponds to
the physical entities where they reside. As illustrated in FIG. 2
on the UTRAN-side (or network side) L2 MAC sub-layer is preferably
located in RNC, whereas L2 MAC-ARQ sub-layer is located in Node B.
Hybrid ARQ protocol combine successively received retransmissions.
It is a great advantage to have the hybrid ARQ protocol close to
the physical layer and, particularly, in Node B. Among the
advantages achieved thereby, e.g., the roundtrip delay is reduced
as compared to a location in RNC. Within this patent application
the protocol layers, except for L2 MAC and L2 MAC-ARQ as just
explained, correspond to those of FIG. 1.
[0056] With reference to FIG. 3, Node B 1 and Node B 2 of a radio
communications system are logical nodes responsible for radio
transmission/reception in one or more cells to/from the User
Equipment UE. BS 1 and BS 2 are physical entities representing Node
B 1 and Node B 2 respectively. Node B 1 and Node B 2 terminate the
air interface, called Uu interface within UMTS, between UE and
respective Node B towards the radio network controller RNC. In UMTS
the interface between a Node B and an RNC is called lub
interface.
[0057] Preferably, all Nodes B of the radio communications system
operate according to the invention for outstanding performance.
However, the invention can also be used in systems also including
Nodes B not operating according to the invention.
[0058] FIG. 4 describes somewhat more detailed than FIG. 2 the
information transfer between the sub-layers of the protocol stack.
In an exemplary situation, and with reference to FIG. 3, UE
communicates over a radio link associated with BS 1. Packet
switched data is transmitted in protocol data units, PDUs, in both
directions. Each PDU is transported on a transport channel in at
least one transport block, TB, as shown in FIG. 4. Preferably there
is one TB for each PDU. As described above, transmission errors on
the transport channel are corrected and detected by layer L1. Each
transport block, TB, in FIG. 4 can be provided an individual CRC
error-detecting checksum prior to transmission on the physical
channel. However, preferably a transmission unit, carrying one or
more TBs, is provided only one CRC error-detecting checksum. If a
transmission unit is detected to be in error on the receiving side,
this is reported to the L2 MAC layer.
[0059] L2 MAC layer can request retransmission of transmission
units received in error. Transmission units, detected to be in
error, still carry information that should not be wasted.
Preferably hybrid ARQ, utilizing information available from earlier
transmission(s) of a transmission unit by proper combining with the
latest retransmission, is used prior to an L2 MAC layer request for
retransmission.
[0060] It is preferred that the Hybrid ARQ is terminated in Node B.
Given L2 RLC located in RNC, the RLC layer should not be
responsible of Hybrid ARQ. According to preferred embodiments of
the invention, an L2 MAC-ARQ sub-layer is responsible of Hybrid
ARQ. At UTRAN-side the L2 MAC-ARQ sub-layer is located in Node
B.
[0061] One reason for terminating the Hybrid ARQ in Node B is the
reduction of roundtrip delay as compared to terminating it in RNC.
Another reason is that Node B is capable of using soft combining of
multiply transmitted data packets, whereas RNC generally only
receives hard-quantized bits.
[0062] At the receiving end, error detection is also performed by
layer L2 RLC of FIG. 4. If an RLC protocol data unit, PDU, is
received in error or the PDU is missing, it will be requested for
retransmission at a point in time when a status report is
established by the RLC layer. RLC PDUs are transferred to/from the
MAC layer SDUs. The MAC SDU (Service Data Unit) possibly includes a
header not included in the RLC PDU. As explained in relation to
FIG. 2, according to the invention there are preferably two UTRAN
MAC sub-layers, an L2 MAC sub-layer and an L2 MAC-ARQ sub-layer. In
a preferred embodiment of the invention, the L2 MAC sub-layer is
located in RNC and the L2 MAC-ARQ sub-layer is located in Node B.
As previously described, the RLC PDUs are transferred in transport
blocks, TBs, on the physical channel. In the uplink direction the
L2 MAC-ARQ layer transfers TBs, possibly after combining of
multiple (re-)transmissions of the respective TBs, indicated to be
error-free to the L2 MAC layer.
[0063] A network layer PDU or L3 PDU can comprise several RLC PDUs,
as illustrated in FIG. 4. RLC PDUs are reassembled into RLC service
data units, RLC SDU, prior to delivery to higher layer PDU. The L3
protocol can be, e.g., the Internet Protocol, IP. Upon reception
from L3, RLC SDUs are segmented into RLC PDUS.
[0064] FIG. 5 gives an overview of the uplink protocol structure
according to the preferred embodiment of the invention.
<<RNC>>, <<Node B 1>>, <<Node B
2>> and <<UE>> have been described in relation to
FIG. 3. <<MAC-ARQ 1>> and <<MAC-ARQ 2>> are
MAC-ARQ protocol layers according to the invention of Nodes B
<<Node B 1>> and <<Node B 2>> respectively.
In User Equipment <<UE>>, an integer number of RLC PDUs
<<1>>, <<2>>, . . . , <<i>> are
segmented into a MAC-layer PDU <<MAC PDU>> adapted for
uplink transmission in one transmission time interval, TTI.
Preferably, uplink transmissions are performed on an enhanced
uplink channel with transmission time intervals shorter than
transmission time intervals of prior art. Each Node B <<Node
B 1>>, <<Node B 2>> (positively) acknowledges
<<ARQ Status>> successfully received MAC PDUs.
Optionally, it may negatively acknowledge <<ARQ
Status>> unsuccessfully received MAC PDUs. The
acknowledgements are transmitted in downlink direction to User
Equipment <<UE>>. With only positive acknowledgements,
if no acknowledgement is received within a predetermined time,
<<UE>> retransmits the unacknowledged MAC PDU,
otherwise <<UE>> cancels the MAC PDU from buffer
storing not yet acknowledged MAC PDUs. With optional negative
acknowledgements the predetermined time period becomes less
critical. However, due to the risk of misinterpreting a negative
acknowledgement as a positive acknowledgment, channel dependent
probability of such misinterpretation needs to be considered for
various channel environments for an optimum selection.
[0065] MAC PDUs received by respective MAC-ARQ protocol layer
<<MAC-ARQ 1>>, <<MAC-ARQ 2>> of Nodes B
<<Node B 1>>, <<Node B 2>> are delivered to
Radio Network Controller <<RNC>>, which re-orders
received MAC PDUs into sequential order. This is needed as, e.g., a
single Node B may obtain successfully transmitted and received MAC
PDUs out of order due to varying number of required retransmissions
of different PDUs. Another exemplary reason is that at handover
involving a plurality of Nodes B, different MAC PDUs of an RLC PDU
are received and (re-)transmitted to RNC at different Nodes B for
assembly in RNC, whereas for downlink transmissions there is only
one transmitting entity (Node B) and one receiving entity (UE).
[0066] A reordering entity in radio network controller
<<RNC>> provides in-sequence delivery of RLC PDUs
<<RLC PDUs>>, received in RNC, to RLC layer
<<RLC>>. Two alternative number sequences for
reordering are considered: [0067] reordering based on RLC sequence
numbers for both UM and AM RLC; or [0068] special sequence numbers
on MAC level.
[0069] Special sequence numbers on MAC level is used for downlink
HS-DSCH. However, if reordering is made in RNC number of sequences
can be reduced if reordering is based on RLC sequence numbers,
keeping transmission overhead at a minimum.
[0070] The risk of receiving duplicate RLC PDUs also needs
consideration. Elimination of duplicate RLC PDUs can be based on
RLC sequence numbers as well. The elimination of duplicate RLC PDUs
also reduces the negative impact of positive acknowledgements being
received as negative acknowledgments in UE, if negative
acknowledgments are made use of.
[0071] Preferably, hybrid ARQ is used, softly combining, if more
than one, successive received (re-)transmissions of each MAC PDU.
An identification of process identity <<ProcessID>> and
an indicator of new data <<NewData>> in addition to
payload <<Payload>> may either be included in data
packets <<MAC PDU>> according to the HARQ protocol as
indicated in FIG. 6 or be handled separately but in association
with payload data, illustrated in FIG. 7. The payload field
<<Payload>> comprises an integer number of RLC PDUs.
The indicator of new data <<NewData>> indicates whether
or not a MAC PDU is a retransmission and is included for control of
soft combining. This may be explicitly indicated, or indicated
implicitly by a sequence number, which is increased for each
transmission of a not earlier transmitted MAC PDU.
[0072] There is need for greater reliability at transmission of
process identity and new data indicator fields
<<ProcessID>>, <<NewData>>, than payload.
If control data is not received, corresponding payload cannot be
soft-decision combined with data of other transmissions. Therefore,
control fields <<ProcessID>> and
<<NewData>> are transferred with higher reliability
than the data channel transferring the payload. The higher
reliability can be achieved by, e.g., more error resistant error
control coding or increased transmission power. Preferably, control
fields for process identity <<ProcessID>> and new data
indicator <<NewData>> are transmitted on a control
channel separate from the data channel. The control and data
channels are synchronized.
[0073] In addition to the control fields mentioned above there are
control fields of nature well known in the art carrying information
on, e.g., number of payload RLC PDUs and transport block size.
[0074] A well-known (one-channel) stop-and-wait ARQ protocol does
not provide sufficient throughput for most studied relevant cases.
According to the invention selective repeat or N-channel
stop-and-wait ARQ is preferred.
[0075] For N-channel stop-and-wait, Node B needs to store soft
samples of up to N different MAC PDUs for each UE. The N channels
are time multiplexed as illustrated in FIG. 8. For a particular
channel, no further data is transmitted until an acknowledgement is
received or time for acknowledgement has elapsed according to a
stop-and-wait protocol. I.e. acknowledgements are scheduled such
that acknowledgement <<1st ACK>> acknowledging data
transmitted in a 1.sup.st channel <<1st channel>>
arrives not later than next transmission instant of 1.sup.st
channel <<1st channel>>. The same holds for 2.sup.nd
channel <<2nd channel>> up to N.sup.th channel
<<Nth channel>>
[0076] FIG. 9 displays an RNC according to the invention. Receive
means 1 receives first protocol data units, e.g. MAC PDUs,
transferred from one or more Nodes B. Received first protocol data
units are stored by buffering means 2. The first protocol data
units are segmented into second protocol data units, e.g. RLC PDUs,
by segmentation means 3. Reorder means 4 operates on the segmented
buffered data units and reorders the second protocol data units as
need be in consecutive order according to a sequence number. For
transfer to higher layers, reassemble means 5 reassembles the
second protocol data units into service data units, which are
transferred by transfer means 6.
[0077] The radio network further comprises processing means 7,
verifying second protocol data units according to an error
detecting code. Acknowledgments, preferably included in status
reports, of second protocol data units are transmitted by transmit
means 8.
[0078] FIG. 10 displays a Node B according to the invention. Node B
transmits responses to UE providing information on the outcome of
data transfers over the radio interface from UE to Node B. In an
example situation receive means 9 receive one or more first
protocol data units, e.g. MAC PDUs, the received first protocol
data units are stored in buffering means 10 and processed in
protocol entity 11 determining, among other things, whether the
received data unit is valid codeword. Transmit means 12 accordingly
acknowledges the received data unit to the sender (UE). When a
multitude of transmissions are required for obtaining a valid
received protocol data unit, the number of (re-)transmissions may
be reduced by properly combining the transmissions. Optional
combining means 13, performs such combining, preferably using soft
decision information from the receive means 9.
[0079] FIG. 11 displays a User Equipment, UE, according to the
invention. Assemble means 14 assembles second protocol data units,
e.g. RLC PDUs, to first protocol data units, e.g. MAC PDUs. The
first protocol data units are buffered by buffering means 15 and
transmitted one or more times, as need be, by transmit means 16. If
transmission is considered successful according to, appeared or
non-appeared, acknowledgements, positive or negative
acknowledgements of first protocol data units are received by
receive means 17.
[0080] Positive or negative acknowledgments of second protocol data
units are received by receive means 18 optionally distinguishing
from receive means 17.
[0081] A person skilled in the art readily understands that the
receiver and transmitter properties of a BS or a UE are general in
nature. The use of concepts such as BS, UE or RNC within this
patent application is not intended to limit the invention only to
devices associated with these acronyms. It concerns all devices
operating correspondingly, or being obvious to adapt thereto by a
person skilled in the art, in relation to the invention. As an
explicit non-exclusive example the invention relates to mobile
stations without a subscriber identity module, SIM, as well as user
equipment including one or more SIMs. Further, protocols and layers
are referred to in close relation with UMTS terminology. However,
this does not exclude applicability of the invention in other
systems with other protocols and layers of similar
functionality.
[0082] The invention is not intended to be limited only to the
embodiments described in detail above. Changes and modifications
may be made without departing from the invention. It covers all
modifications within the scope of the following claims.
* * * * *