U.S. patent application number 11/110364 was filed with the patent office on 2006-03-02 for data communications apparatus for cable network.
Invention is credited to David S. H. Lee.
Application Number | 20060045002 11/110364 |
Document ID | / |
Family ID | 35942900 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060045002 |
Kind Code |
A1 |
Lee; David S. H. |
March 2, 2006 |
DATA COMMUNICATIONS APPARATUS FOR CABLE NETWORK
Abstract
A data communications apparatus which uses the same frequency
band and modulation scheme with those used in the counterpart
apparatus, and has a simple configuration and shows high
reliability in transmitting and receiving high-rate data through a
cable network. The main processing unit receives the first data
from the data processing device to perform orthogonal frequency
division multiplexing (OFDM) on the first data to generate first
OFDM signal, and demultiplexes second OFDM signal from the
counterpart apparatus to recover the second data and provide to the
data processing device. The RF unit transforms the first OFDM
signal into a radio frequency band to generate the first modulated
signal and transmit to the counterpart apparatus through the second
port and the cable network. Also, the RF unit receives the second
modulated signal from the counterpart apparatus to recover a second
OFDM signal and provide to the main processing unit. The medium
access control performing means detects collision in the cable
network and selectively activates the main processing unit so that
the RF unit transmits and receives signal to and from the
counterpart apparatus through a common cable line.
Inventors: |
Lee; David S. H.;
(Seocho-gu, KR) |
Correspondence
Address: |
LAHIVE & COCKFIELD, LLP.
28 STATE STREET
BOSTON
MA
02109
US
|
Family ID: |
35942900 |
Appl. No.: |
11/110364 |
Filed: |
April 19, 2005 |
Current U.S.
Class: |
370/208 ;
370/445 |
Current CPC
Class: |
H04L 1/0668 20130101;
H04L 27/2601 20130101; H04L 1/0643 20130101 |
Class at
Publication: |
370/208 ;
370/445 |
International
Class: |
H04L 12/413 20060101
H04L012/413; H04J 11/00 20060101 H04J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2004 |
KR |
2004-70119 |
Claims
1. A data communications apparatus, connected to a data processing
device through a first port and connected to a counterpart
apparatus through a second port and cable network, for receiving
first data from the data processing device and modulate the first
data to transmit first modulated signal to the counterpart
apparatus and receiving second modulated signal from the
counterpart apparatus and demodulate the second modulated signal to
recover second data and provide to the data processing device, said
data communications apparatus comprising: a main processing unit
for receiving the first data from the data processing device to
perform orthogonal frequency division multiplexing (OFDM) on the
first data to generate first OFDM signal, and demultiplexing second
OFDM signal from the counterpart apparatus to recover the second
data and provide to the data processing device; a RF unit for
transforming the first OFDM signal into a radio frequency band to
generate the first modulated signal and transmit to the counterpart
apparatus through said second port and the cable network, and
receiving the second modulated signal from the counterpart
apparatus to recover a second OFDM signal and provide to said main
processing unit; and means for performing medium access control to
detect collision in the cable network and selectively activate said
main processing unit so that said RF unit transmits and receives
signal to and from the counterpart apparatus through a common cable
line.
2. The apparatus as claimed in claim 1, wherein said medium access
control performing means comprises: a MAC unit electrically
connected to said first port and including a buffer for buffering
the first data provided to said main processing unit; and a
half-duplex controller for determining availability of the cable
network and controlling said MAC unit.
3. The apparatus as claimed in claim 2, wherein said main
processing unit comprises: a quadrature amplitude
modulator/demodulator for performing quadrature amplitude
modulation on the first data from the MAC unit to generate first
QAM signal and demodulating second QAM signal to recover the second
data; and an OFDM unit for performing OFDM on the first QAM signal
to generate the first OFDM signal, and demultiplexing second OFDM
signal to recover the second QAM signal.
4. The apparatus as claimed in claim 3, wherein said main
processing unit further comprises: an error-correction encoder for
error-correction encoding the first data from the MAC unit to
provide first error-correction encoded data to said quadrature
amplitude modulator/demodulator; and an error-correction decoder
for receiving second error-correction encoded data from the first
data from said quadrature amplitude modulator/demodulator to
recover the second data and provide to said MAC unit.
5. The apparatus as claimed in claim 2, wherein said half-duplex
controller controls the MAC unit by a Distribution Coordination
Function of CSMA/CA mode and centrally-controlled Point
Coordination Function.
6. The apparatus as claimed in claim 2, wherein said MAC unit
communicates with the data processing device in data frame
compliant with IEEE 802.11 standard.
7. The apparatus as claimed in claim 1, wherein said RF unit
comprises: a modulating and detecting unit for modulating the first
OFDM signal to the first modulated signal and detecting the second
OFDM signal from the second modulated signal; and a RF transformer
for amplifying and filtering the first modulated signal to transmit
to the counterpart apparatus, and filtering and amplifying signal
received through said second port and the cable network to provide
the second modulated signal to said modulating and detecting
unit.
8. The apparatus as claimed in claim 1, wherein said first port
comprises an optical transceiver providing connection to the data
processing device.
9. The apparatus as claimed in claim 1, wherein the cable network
includes a plurality of taps operating in frequency band below 2.5
GHz.
10. The apparatus as claimed in claim 9, wherein the taps operates
in frequency band below 1 Ghz.
11. A system for providing a predetermined service in a state of
being connected to Internet, comprising: a networking unit for
connecting to the Internet; and a service module coupled to the
networking unit for transmitting and receiving data to and from the
Internet through the networking unit to provide the service,
wherein said networking unit is connected to an external
counterpart unit through a network and cable network for receiving
first data from the service module modulating the first data to
transmit first modulated signal to the external counterpart unit,
and receiving second modulated signal from the external counterpart
unit and demodulating the second modulated signal to recover second
data and provide to the service module, wherein said networking
unit comprises: a main processing unit for receiving the first data
from the service module to perform orthogonal frequency division
multiplexing (OFDM) on the first data to generate first OFDM
signal, and demultiplexing second OFDM signal from the external
counterpart unit to recover the second data and provide to the
service module; a RF unit for transforming the first OFDM signal
into a radio frequency band to generate the first modulated signal
and transmit to the external counterpart unit through said port and
the cable network, and receiving the second modulated signal from
the external counterpart unit to recover a second OFDM signal and
provide to said main processing unit; and means for performing
medium access control to detect collision in the cable network and
selectively activate said main processing unit so that said RF unit
transmits and receives signal to and from the external counterpart
unit through a common cable line.
12. The system as claimed in claim 11, wherein said service module
is a VoIP service module.
13. The system as claimed in claim 11, wherein said service module
is a settop box service module.
14. The system as claimed in claim 11, wherein said service module
is a wireless LAN service module.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a data communications
apparatus and, more particularly, a data communications apparatus
capable of performing bidirectional data communications through a
cable network. This application for a communications apparatus is
based on Korean patent application No. 2004-70119, which is
incorporated by reference herein for all purposes.
[0003] 2. Description of the Related Arts
[0004] The most common methods for implementing high-speed Internet
subscriber network include the use of a DSL modem or a cable modem,
which transmits and receives digital data through an existing
twisted wire pair or a cable TV network, respectively. While the
DSL modem is cost-effective in case that cable TV lines are broadly
installed to a large majority of residences, the cable modem may be
more effective alternative if cable TV lines are available in most
of the residences. In a data communications network based on the
cable TV network, each subscriber premise is connected to or
equipped with a cable modem, which communicates with a counterpart,
i.e., a headend to help the subscriber premise with Internet
access.
[0005] FIG. 1 illustrates an example of a data communications
system based on the cable TV network. In the system shown in FIG.
1, a headend or a cable modem termination system (CMTS) 10 is
connected to a plurality of cable modems 34A, 34B through a tap 20
and/or a splitter 30. The CMTS 10 is connected to an Internet
service provider (ISP) server 12, and the cable modems 34A, 34B are
connected to client PCS 36A, 36B, respectively. The CMTS 10
modulates data to be transmitted from the ISP server 12 to a client
PC 34A or 34B to transmit through the cable network, so that a
desired cable modem 34A, for example, demodulates such data to
provide to the client PC 34A. Similarly, the cable modem 34A
modulates data generated by the client PC 34A to transmit to the
CMTS 10, so that the CMTS 10 demodulates such data to provide to
the ISP server 12.
[0006] Generally, a cable network equipment is manufactured to be
compliant with Data Over Cable Service Interface Specification
(DOCSIS) proposed by Multimedia Cable Network System (MCNS) and
IEEE802.14 standard proposed by Institute of Electronic and
Electrical Engineering (IEEE). According to the DOCSIS standard,
the CMTS modulates the downstream data by 64 Quadrature Amplitude
Modulation (QAM) or 256 QAM scheme in a frequency band of 5 MHZ to
45 MHZ to provide a data rate of 20 Mbps to 30 Mbps. The cable
modem modulates the upstream data by Quadrature Phase Shift Keying
(QPSK) or 16 QAM scheme in a frequency band of 65 MHZ to 750 MHZ to
provide a data rate of 200 Kbps to 10 Mbps. Meanwhile, regarding
medium access control (MAC), frequency domain multiple access
(FDMA)/time division multiplexing (TDM) is used to facilitate
communication from the CMTS to each cable modem and FDMA/time
domain multiple access (TDMA) is used to facilitate communication
from each cable modem to the CMTS.
[0007] However, the conventional CMTS and cable modem adopting FDMA
or TDMA along with TDM are disadvantageous in that it is difficult
for them to provide high data rates, for example, above 50 Mbps.
Besides, the conventional CMTS and cable modem has drawbacks that
they are much complex in their hardware configuration and show less
reliability because different frequency bands and modulation
schemes are used for the transmission of upstream and downstream
data.
SUMMARY OF THE INVENTION
[0008] To solve the above problem, one object of the present
invention is to provide a data communications apparatus which uses
the same frequency band and modulation scheme with those used in
the counterpart apparatus, and has a simple configuration and shows
high reliability in transmitting and receiving high-rate data
through a cable network.
[0009] The data communications apparatus for achieving the above
object is connected to a data processing device through a first
port and connected to a counterpart apparatus through a second port
and cable network. The apparatus receives first data from the data
processing device and modulates the first data to transmit first
modulated signal to the counterpart apparatus, and receives second
modulated signal from the counterpart apparatus and demodulate the
second modulated signal to recover second data and provide to the
data processing device.
[0010] The data communications apparatus includes a main processing
unit, a RF unit, and medium access control performing means. The
main processing unit receives the first data from the data
processing device to perform orthogonal frequency division
multiplexing (OFDM) on the first data to generate first OFDM
signal, and demultiplexes second OFDM signal from the counterpart
apparatus to recover the second data and provide to the data
processing device. The RF unit transforms the first OFDM signal
into a radio frequency band to generate the first modulated signal
and transmit to the counterpart apparatus through the second port
and the cable network. Also, the RF unit receives the second
modulated signal from the counterpart apparatus to recover a second
OFDM signal and provide to the main processing unit. The medium
access control performing means detects collision in the cable
network and selectively activates the main processing unit so that
the RF unit transmits and receives signal to and from the
counterpart apparatus through a common cable line.
[0011] Preferably, the medium access control performing means
includes a MAC unit electrically connected to the first port and
including a buffer for buffering the first data provided to the
main processing unit; and a half-duplex controller for determining
availability of the cable network and controlling the MAC unit. It
is preferable that the main processing unit includes a quadrature
amplitude modulator/demodulator and an OFDM unit. The quadrature
amplitude modulator/demodulator performs quadrature amplitude
modulation on the first data from the MAC unit to generate first
QAM signal and demodulating second QAM signal to recover the second
data. The OFDM unit performs OFDM on the first QAM signal to
generate the first OFDM signal, and demultiplexes second OFDM
signal to recover the second QAM signal. The main processing unit
preferably further includes an error-correction encoder and an
error-correction decoder. The error-correction encoder
error-correction encodes the first data from the MAC unit to
provide first error-correction encoded data to the quadrature
amplitude modulator/demodulator. The error-correction decoder
receives second error-correction encoded data from the first data
from the quadrature amplitude modulator/demodulator to recover the
second data and provide to the MAC unit.
[0012] Preferably, the half-duplex controller controls the MAC unit
by a Distribution Coordination Function of CSMA/CA mode and
centrally-controlled Point Coordination Function. Also, the MAC
unit communicates with the data processing device in data frame
compliant with IEEE 802.11 standard.
[0013] The RF unit may include a modulating and detecting unit and
a RF transformer. The modulating and detecting unit modulates the
first OFDM signal to the first modulated signal and detects the
second OFDM signal from the second modulated signal. The RF
transformer amplifies and filters the first modulated signal to
transmit to the counterpart apparatus, and filters and amplifies
signal received through the second port and the cable network to
provide the second modulated signal to the modulating and detecting
unit.
[0014] It is preferable, but not limited to, that the apparatus
operates in frequency band below 2.5 GHZ. More preferably, the
apparatus operates in frequency band below 1 GHz.
[0015] By employing the OFDM scheme having been used typically in
wireless communications system along with half-duplex communication
mode (for example, IEEE802.11 compliant medium access control
mechanism), the inventor have found that the communications system
of the present invention accomplish data rate higher than 50 MHz.
Also, the apparatus of the present invention enhances the
efficiency of frequency bandwidth because data transmission is
performed in the same frequency as that used in the reception.
Further, the simple architecture of the apparatus can reduce the
system purchasing or deploying cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above objects and advantages of the present invention
will become more apparent by describing in detail preferred
embodiments thereof with reference to the attached drawings in
which:
[0017] FIG. 1 illustrates an example of a data communications
network based on a cable TV network;
[0018] FIG. 2 illustrates an embodiment of a data communications
network of the present invention;
[0019] FIG. 3 is a schematic diagram showing a preferred embodiment
of the OFDM termination system and one of the OFDM modems shown in
FIG. 3;
[0020] FIG. 4 shows the frame format specified in IEEE 802.11
standard;
[0021] FIG. 5 is a detailed block diagram of the QAM unit, the OFDM
unit, and the RF unit of the OFDM termination system shown in FIG.
3;
[0022] FIG. 6 illustrates an example of implementation of the OFDM
termination system;
[0023] FIG. 7 illustrates an example of implementation of the OFDM
modem; and
[0024] FIGS. 8A through 8C illustrates another embodiments of the
data communications apparatus of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Referring to FIG. 2, a data communications system of the
present invention may be implemented based on a cable network. The
data communications system includes an OFDM termination system 100
and OFDM modems 140A, 140B each for respective subscriber and
connected to the OFDM termination system 100 through a cable
network. The OFDM termination system 100 functionally corresponds
to the conventional CMTS 10 shown in FIG. 1, and OFDM modems 140A,
140B correspond to the cable modems 34A, 34B, respectively.
[0026] The OFDM termination system 100 is connected to the OFDM
modems 140A, 140B by coaxial cable lines 112, 114, 116 of the cable
network through a tap 110 and/or a splitter 120. The coaxial cable
network represented by the coaxial cable lines 112, 114, 116 may
partially be implemented by a hybrid fiber coax (HFC) network. The
OFDM termination system 100 is connected to an Internet service
provider (ISP) server 12 through optical cable or unshielded
twisted pair (UTP) cable, and the OFDM modems 140A, 140B are
connected to client PCS 142A, 142B, respectively, through UTP cable
or USB cable. The tap 110 divides and combines signals to and from
several residences so as to accommodate a large number of
subscribers, and the splitter 120 enables a television receiver and
the client PC to share a single cable TV line.
[0027] In a preferred embodiment, the OFDM termination system 100
modulates data to be transmitted from the ISP server 102 to one of
the client PCS 34A, 34B by QAM and OFDM schemes to transmit through
the cable network, so that a desired OFDM modem 140A, for example,
demodulates such data to provide to the client PC 142A. Similarly,
the OFDM modem 140A modulates data generated by the client PC 142A
by QAM and OFDM schemes to transmit to the OFDM termination system
100 through the cable network, so that the OFDM termination system
100 demodulates such data to provide to the ISP server 102. Thus,
the system of FIG. 2 has a point-to-multipoint topology and
facilitates the bidirectional communications between the ISP server
10 and the client PCS 142A, 142B.
[0028] FIG. 3 is a schematic diagram of an embodiment of the OFDM
termination system 100 and the OFDM modem 140A.
[0029] The OFDM termination system 100 includes a MAC 200, a main
processing unit 210, and a RF unit 270. The MAC 200 decapsulates
Ethernet packets received from the ISP server 102 and encapsulates
data to be transmitted to the ISP server 102 into Ethernet packets.
Also, the MAC 200 includes a first in first out (FIFO) buffer, and
temporarily stores data to be modulated by the main processing unit
210, so that the modulation process of the main processing unit 210
is mediated while avoiding data collision in the coaxial line. The
main processing unit 210 receives, from the MAC 210, data to be
transmitted to the OFDM modem 140A to modulate by QAM and OFDM
schemes, demodulates signal received from the OFDM modem 140A, and
supports half-duplex communication by detecting and avoiding data
collision in the coaxial line based on the received signal. The RF
unit 270 upconverts the frequency band of the modulated signal into
the RF band to transmit to the OFDM modem 140A, and downconverts
the frequency band of signal received from the OFDM modem 140A to
provide to the main processing unit 210.
[0030] The main processing unit 210 includes a QAM unit 220, an
OFDM unit 240, and a half-duplex controller 265. The QAM unit 220
performs QAM process for the data received from the MAC 200, and
the OFDM unit spreads the spectrum of the QAM signal by performing
inverse Fast Fourier Transform (IFFT) with respect to the signal.
The half-duplex controller 265 determines the busy status of the
transmission medium, i.e., the coaxial line based on the signal
received through the RF unit 270, and controls the input and output
of the MAC 200 depending on the determination result. In case that
the medium is not being used, data is allowed to transfer from the
MAC 200 to the main processing unit 220. the medium is being used,
however, the data transfer from the MAC 200 to the main processing
unit 220 is inhibited. By repetitively controlling the operation of
the MAC 200, the half-duplex controller 265 enables the half-duplex
communications.
[0031] Similarly, the OFDM modem 140A includes a MAC 300, a main
processing unit 310, and a RF unit 380. The MAC 300 decapsulates
Ethernet packets received from the client PC 142A and encapsulates
data to be transmitted to the client PC 142A into Ethernet packets.
Also, the MAC 300 includes a first in first out (FIFO) buffer, and
temporarily stores data to be modulated by the main processing unit
310, so that the modulation process of the main processing unit 310
is mediated while avoiding data collision in the coaxial line. The
main processing unit 310 receives, from the MAC 310, data to be
transmitted to the OFDM termination system 100 to modulate by QAM
and OFDM schemes, demodulates signal received from the OFDM
termination system 100, and supports half-duplex communication by
detecting and avoiding data collision in the coaxial line based on
the received signal. The RF unit 380 upconverts the frequency band
of the modulated signal into the RF band to transmit to the OFDM
termination system 100, and downconverts the frequency band of
signal received from the OFDM termination system 100 to provide to
the main processing unit 310. Since the configuration and operation
of the main processing unit 310 are similar to those of unit 210,
detailed description thereof is omitted.
[0032] Preferably, the OFDM termination system 100 and the OFDM
modem 140A of the present invention use frame format specified in
IEEE 802.11. FIG. 4 shows the frame format of IEEE 802.11, which
format is applied to all the frames transmitted between the OFDM
termination system 100 and the OFDM modem 140A regardless of the
type of frames. The frame shown in the drawing is comprised of a
frame header 402, a frame body 404, and a frame check sequence
(FCS) 406.
[0033] IEEE 802.3 compliant Ethernet packets transferred from the
OFDM termination system 100 or the OFDM modem 140A are mapped into
the variable-length frame body 404 as payloads. The frame body 404
is preceded by the frame header 402, which consists of following
components: FRAME CONTROL field, DURATION/ID field indicating back
off time which depends on the transferred frame, ADDRESS1 to
ADDRESS4 fields depending on the type of the transferred frame, and
SEQUENCE CONTROL field. The FRAME CONTROL field consists of
PROTOCOL VERSION field, DATA TYPE field, SUBTYPE field, TO DS
field, FROM DS field, MORE FRAG field, RETRY field, POWER
MANAGEMENT field, MORE DATA field, WEB field, and ORDER field.
Meanwhile, a 32-bit wide frame check sequence is calculated based
on cyclic redundancy code (CRC) and appended behind the frame body
404 as the frame check sequence (FCS) 406.
[0034] In addition to the frame format of IEEE 802.11, the OFDM
termination system 100 and the OFDM modem 140A preferably use the
medium access control (MAC) mechanisms specified in IEEE 802.11:
(1) the basic access mechanism referred to as the Distributed
Coordination Function (DCF) based on Carrier-Sense Multiple Access
with Collision Avoidance (CSMA/CA), and (2) a centrally-controlled
access mechanism referred to as the Point Coordination Function
(PCF) based on polling.
[0035] In DCF mechanism, a station, i.e., the OFDM termination
system 100 or the OFDM modem, willing to transmit data packet first
transmits a short control packet in a contention period before
sending the data packet in order to determine whether another
station is transmitting data over the desired channel. The station
receives the signal in the channel just after sending the control
packet and determines whether a collision has occurred in the
channel by finding a signal other than that sent by itself. In case
that the medium is free for a specified time, then the station is
allowed to transmit the data packet. If a collision occurred,
however, the station defers the transmission of the data packet and
retries the transmission after a random backoff time.
[0036] In PCF mechanism which is an optional mode for allowing the
transmission of time-bounded and contention-free frames, the OFDM
termination system 100 plays the role of a point coordinator. At
the beginning of a contention-free period, the OFDM termination
system 100 has a chance of obtaining coordination authority. In
this operation mode, medium access of all the OFDM modems connected
to the cable network is controlled by the OFDM termination system
100.
[0037] FIG. 5 illustrates, in detail, the QAM unit 220, the OFDM
unit 240, and the RF unit 270 of the OFDM termination system 100
shown in FIG. 3.
[0038] The QAM unit 220 includes a forward-error-correction (FEC)
encoder 222, an interleaver 224, a QAM mapping unit 226, a QAM
demapping unit 228, a deinterleaver 232, and a FEC decoder 234. The
FEC encoder 222 error-correction-codes transmit data to enhance the
error robustness, and the interleaver 224 interleaves the
error-correction-coded data so as to change an burst error which
may be introduced in the channel into random errors. The QAM
mapping unit 226 performs 16 QAM operation, for example, on the
interleaved data to generate 16 QAM I and Q signals and provide to
the OFDM unit 240. The QAM demapping unit 228, the deinterleaver
232, and the FEC decoder 234 perform inverse processes of the
processes performed by the counterparts equipped with the OFDM
modem 140A similarly to the FEC encoder 222, the interleaver 224,
and the QAM mapping unit 226, thereby restoring the data sent by
the client PC 142A.
[0039] In the OFDM unit 240, a pilot insertion unit 242 inserts
pilot symbols into the QAM symbol sequence from the QAM unit 320. A
serial-to-parallel converter 242 converts the symbol sequence
inserted with the pilot symbols into parallel format. An IFFT block
246 performs IFFT operation on parallel symbol sequences to spreads
the frequency band and form OFDM symbols. A parallel-to-serial
converter 248 converts the parallel OFDM symbols back to serial
format. A cyclic extension adder 250 adds a cyclic prefix to the
OFDM symbols. Meanwhile, a cyclic extent remover 252 removes, from
the received signal, the cyclic prefix added by the OFDM modem
104A. A serial-to-parallel converter 254 converts prefix-removed
data into parallel format. A FFT block 256 performs FFT operation
on parallel data from the serial-to-parallel converter 254 to
despread the received OFDM symbols. A parallel-to-serial converter
258 converts the despreaded data back to serial format. A channel
correction unit 260 removes pilot symbols from the despreaded QAM
symbol sequence.
[0040] In the RF unit 270, IQ modulator 272 modulates the carrier
of 40 MHZ from an oscillator 274 to 16 states with the OFDM IQ
symbols. A upconverter 276 upconverts the frequency band of the
modulated signal using the signal of 22 MHZ from an oscillator 278.
A high power amplifier (HPA) 280 amplifies the upconverted signal,
and a bandpass filter (BPF) 282 filters the amplified signal by
selectively passing desired frequency bands to transmit through the
cable network.
[0041] A BPF 284, having the same pass band as the BPF 282
bandpass-filters the signal received through the cable network. A
low noise amplifier 286 amplifies the filtered signal, and a
downconverter 288 downverts the frequency band of the amplified
signal using the signal of 22 MHZ from the oscillator 278. An
automatic gain control (AGC) amplifier 290 amplifies the
downconverted signal depending on the intensity of the
downconverted signal. An IQ detector 292 demodulates the amplified
signal using the signal of 40 MHZ from an oscillator 294 to recover
the OFDM I and Q symbols. The output signal of the oscillator 274
is controlled by an clock recovery unit 296. A timing and frequency
synchronizer 298 controls timing and frequency of the demodulated
signal.
[0042] On the other hand, the QAM unit 320, the OFDM unit 340, and
the RF unit 370 of the OFDM modem 140A have the same configuration
as those of the OFDM termination system 100, and thus the OFDM
termination system 100 and the OFDM modem 140A operates
symmetrically.
[0043] FIG. 6 illustrates an example of implementation of the OFDM
termination system 100. The OFDM termination system 100 may be
implemented using a microcontroller 300 having an embedded CPU, and
a radio chip 410. The MAC unit 200 and the main processing unit is
implemented by program executed by the microcontroller 400. In this
example, the microcontroller 400 is connected to an Ethernet
transceiver 402 and/or an optical transceiver 404. The Ethernet
transceiver 402 and the optical transceiver 404 are connected to
the ISP server 102 by twisted pair 403 and optical fiber 405,
respectively. Also, the OFDM termination system 100 is connected to
the cable network through a F-connector 416.
[0044] FIG. 7 illustrates an example of implementation of the OFDM
modem 140A. In this example, the OFDM modem 140 has the same
configuration as that of the OFDM termination system 100 of FIG. 6
except that a USB transceiver 440 may be used instead of the
optical transceiver.
[0045] The frequency band for the operation of the communication
devices is limited typically by the characteristics of the
transmission medium and the taps. The OFDM termination system 100
and the OFDM modem 140A may be used in the frequency band below 2.5
GHZ preferably in consideration of the signal transferring
capability of the taps, and below 1 GHZ more preferably.
[0046] While the OFDM termination system or the OFDM modem can be
manufactured and used in stand-alone type, such an apparatus can be
employed in an application system which requires an network
connection capability. FIGS. 8A through 8C shows such alternative
embodiments of the present invention.
[0047] In FIG. 8A, the OFDM modem 500 is employed in a voice over
Internet Protocol (VoIP) system 510 to enable the system 510 to
access Internet through the cable network. With the assistance of
the OFDM modem 500, a VoIP service module 512 which includes
protocol stacks and user interfaces provides VoIP service to the
user. The configuration of the OFDM modem 500 is similar to that
shown in FIG. 3 except that the modem 500 may be directly coupled
to the VoIP sercive module 512.
[0048] In FIG. 8B, the OFDM modem 500 is employed in a settop box
system 520 for providing video on demand (VOD) service through the
Internet. In the system of FIG. 8B, a settop box service module 522
which includes protocol stacks and user interfaces communicates an
appropriate Internet server to provide VOD service to the user.
[0049] In FIG. 8C, the OFDM modem 500 is employed in a wireless LAN
access point (AP) 530 for facilitating wireless terminals to access
Internet. In the system of FIG. 8C, a wireless LAN service module
522 which includes RF circuits and protocol stacks communicates
with the OFDM modem communicates in data frames compliant with IEEE
802.11 standard.
[0050] Although the present invention has been described in detail
above, it should be understood that the foregoing description is
illustrative and not restrictive. Those of ordinary skill in the
art will appreciate that many obvious modifications can be made to
the invention without departing from its spirit or essential
characteristics. We claim all modifications and variation coming
within the spirit and scope of the following claims.
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