Forward error correction scheme in a wireless system

(74) Agent

IPR Licensing Inc, 3411 Silverside Road, Concord Plaza, Suite 105 Hagley Building, US-DE19810 WILMINGTON, USA

James A Proctor Jr., 440 Mosswood Boulevard, US-FL32903-4007 INDIALANTIC, USA

Bryn Aarflot AS, PO Box 449 Center, 0104 OSLO, Norway

<td> (54)</td><td>Designation</td><td>Error correction method in a wireless system</td>

<td> (56)</td><td>cited</td><td></td>

<td></td><td>publications</td><td>WO 9843373 A1</td>

<td> (57)</td><td>Summary</td><td></td>

High-speed data transmitter / receiver equipment in a wireless communications system comprises a physical layer processor comprising an FEC encoder, a demultiplexer, and several modem processors. The FEC encoder applies error correction codes to the high data rate data signal. The demultiplexer then distributes portions of the high data rate encoded data signal to the various modem processors. Each modem processor then processes its respective portion of the encoded signal for transmission over an assigned independent channel.

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BACKGROUND

The present invention relates to a low latency error correction mechanism and too high data transmission rate across multiple traffic channels within a wireless communication system.

WO 99/14878 A1 and WO 98/43373 A1 indicate the nearest technique.

It is known to include forward error correction coding (FEC) and decoding of information signals to be transmitted over a wireless channel. Forward error correction generally introduces predetermined redundancy in an information signal to enable a receiver to identify and possibly correct errors that may have been caused by a transmission medium. The well-known IS-95 standard for code-sharing multiple-cell communication specifies e.g. a type of envelope code for each traffic channel used for transfer from a base station to a mobile station or vice versa.

Recently, it has been proposed to provide high-speed data exchange over a wireless communications system. Such high-speed data exchange can e.g. is used to facilitate data transfer for data processing applications or for video conferencing applications. Within such a proposed scheme, a high data rate signal can be communicated to a receiver over several parallel traffic channels. The recently proposed IS-95 B standard suggests e.g. use of parallel CDMA channels, each having a data rate of 9.6 KB / s, thereby creating high data rate communication. Within such equipment, a high data rate signal is demultiplexed into multiple data signals with lower data rate, and each of these signals is then processed in an independent traffic channel. FEC has then been applied to each of these data signals with lower data rates.

Another example of a CDMA wireless system that uses multiple parallel traffic channels for high-speed data exchange can be found in the concurrent patent application entitled Protocol Conversion and Bandwidth Reduction Technique Providing Multiple nB + D ISDN Basic Rate Interface Links Over a Wireless Code Division Multiple Access Communication System, with serial no. 09 / 030,049, filed February 24, 1998, the contents of which are incorporated herein by reference.

Wireless communication channels have an inherent tendency to be noisy due to. channel interference caused by atmospheric conditions, multi-path effects, inter-channel interferences, etc. Especially if the transmission is used for data processing applications, where execution instructions can be expected to be exchanged over traffic channels, the need for effective FEC technology will still be important.

Using more efficient FEC techniques in such wireless transmission systems can then increase the latency of data orders. The known turbo codes require e.g. receiving large data blocks alone and by a decoder before decoding can begin. The latency period generally applies to the time delay that runs from the time a data order is issued by a user and to the time when data in accordance with that order is available to the user. FEC introduces decoding delays in a wireless receiver and thus contributes to latency.

There is a need in the field of wireless communication equipment that will be able to conduct high-speed data exchange with high-quality FEC as well as low latency.

SUMMARY

Embodiments of the present invention create a high data rate transmitter / receiver system within a wireless communication system where a physical layer processor comprises an FEC encoder, a demultiplexer, and several modem processors. The FEC encoder applies error correction codes to the high data rate signal. Then, the demultiplexer distributes portions of the high data rate coded signal on the modem processors. Each modem processor processes its assigned portion of the encoded signal for transmission over its own channel.

The main features of the invention are apparent from the independent claims. Further features of the invention are set forth in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached figure shows a transmitter and a receiver, each of which is embodied in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

The present invention relates to low latency forward error correction for high data rate wireless transmission by applying forward error correction codes to the relevant data prior to multiplexing data distributed across multiple parallel bandwidth traffic channels.

The attached figure is a block diagram of a transmitter 100 and a receiver 200, each constructed in accordance with the embodiment of the present invention. The transmitter 100 and receiver 200 are shown for operation in a layered communication system comprising a transmission layer 110, 210, a physical layer 120, 220 and higher communication layers, such as network layer &amp; data transfer layer (collectively designated 130 &amp; 230). As will be known, a transmitter 100 in the transmission layer 110 performs carrier wave modulation, amplification, and transmission of data signals to be transmitted. As will also be known, a receiver 200 in the transmission layer 210 performs reception, amplification and carrier demodulation to derive a recovered digital data signal. The higher layers 110, 210 of the communication system may also process an information signal in the manner required for the application for which the present invention is to be used.

Acc. In one embodiment of the present invention, the physical layer 120 of the transmitter 100 may comprise an FEC encoder 122, a demultiplexer 124, and several modem processors 126a-126n. The number of modem processors 126a-126n may vary and may also be determined by the amount of data to be transmitted and the transmission capacity of each of the traffic channels over which the data can be transmitted. FEC encoder 120 receives a source signal from a higher layer 110 in the transmitter and enriches this signal with an error correction code. The enriched information signal Is is output from the FEC encoder 122 to the demultiplexer 124. The multiplexer distributes this information signal to the modem processors 126a-126n. These modem processors 126a-126n each format their respective portion of the enriched signal for signal transmission. The output signals from modem processors 126a-126n are summed in an adder 128 and output to the transmission layer 110.

In receiver 200, physical layer 220 performs the data processing which is the inverse of the processing applied to physical layer 120 in transmitter 100. This physical layer 220 may comprise an FEC decoder 222, a demultiplexer 224, and several demodulators 226a. 226n. There will then be a demodulator 226a-226n for each of the traffic channels that has been assigned to forward the information signal. The recovered digital signal from the transmission layer 230 constitutes the input signal to each of the demodulators 226a-226n. Each demodulator 226a-226n outputs a recovered portion of the information signal. Demultiplexer 224 combines each of the recovered portions of the information signal into a uniformly recovered information signal. FEC decoder 222 performs error detection and correction using error correction codes applied by FEC encoder 122 in transmitter 100. This FED decoder 222 then outputs a corrected information signal to the higher layers 210 of the receiver 200.

In a CDMA embodiment shown in the figure, a receiver 200 need not include an element corresponding to the adder 128 in the transmitter 100, the demodulators 226a-226n each performing correlation. As will be known, correlation allows a modem processor to discriminate a desired CDMA signal from other CDMA signals that may be present in an aggregate received signal. Thus, in the embodiment shown in the figure, demodulators 226a-226n will be able to identify and output each respective portion of the recovered enriched information signal.

Acc. In some embodiments of the present invention, the FEC encoder 122 and the FEC decoder 222, respectively. generate and decode repeated systematic stacked codes, which will also be known as turbo codes. These turbo codes provide an advantage in that the FEC decoding process can be repeated several times to improve the information signal recovered from the decoding process. Thus, if the output of a first repetition can be reintroduced into the FEC decoding block (the path not shown in the figure) for subsequent repetitions. Acc. of its kind, the turbo tags generate enhanced corrected data for each subsequent repetition.

However, the known turbo codes introduce a predetermined degree of latency into the decoding process. Turbo codes work on blocks of predetermined size. A turbo code intended for a wireless communication system to be used in conjunction with computer networks comprises e.g. a block size of 4,096 channel symbols. An FEC decoder 222 must decode a block in its entirety before a recovered information signal becomes available to the block. This property may be in contrast to enveloped codes used in accordance with the known IS-95 standard for CDMA cellular communication, where convolutional codes are characterized by a relatively small latency for a block of the same size (relative to turbo codes), because then it will not be necessary to receive a block in full before decoding can begin. It is assumed that by distributing the FEC code among the several parallel traffic channels, as shown in the figure, the higher aggregate throughput for the traffic channels will improve the latency that would otherwise be introduced from the turbo code.

For use with high data rates and use of parallel traffic channels, it is then assumed that the use of turbo codes makes it possible to achieve a higher quality number (lower Eb / N₀ than for enveloped codes). Using the example with a block of 4,096 channel symbols and Eb / N₀at 1.5 dB then the turbo code will have a BER value of 10^-6. For voice systems that require a less stringent BER value of 10 '³, a convolutional code will require an Eb / N₀ of 7 dB or more.

The technique according to The present invention finds application in many different wireless communication systems, including CDMA systems. In practice, the base stations and the subscriber stations of the wireless communication system will usually include the functionality of both the transmitter and the receiver in the figure. That is, in order to establish bidirectional communication, a base station must include a transmitter portion 100 and a receiver portion 200. This will also relate to the subscriber terminal. However, the base stations and subscriber terminals need not be configured to provide simultaneous complete duplex communication.

Typically, a base station in a wireless communications system will transmit multiple data signals to many different subscribers simultaneously. Acc. a certain embodiment of the present invention, then each base station may perform the processes set forth herein simultaneously on a plurality of high transmission rate data signals. It is then in accordance with the idea content and scope of the present invention that each signal may have a data rate independent of the data rates of the other signals. In such a case, a base station may be designed to include its FEC encoder / decoder 122, 222 as well as modem processor / demodulators 126a, 226a in a merged configuration. Such an embodiment then enables the base station e.g. assigning a varying number of modem processors 126a-126n to a data signal according to the data rate or rate of the signal to be transmitted. Similarly, by including a composite unit of FEC encoders 122 (shown individually in FIG. 1) in a base station, this base station will be able to selectively activate FEC encoders 122 as the base station receives new data signals to be transmitted to subscribers. The creation of a base station comprising components of a summarized arrangement will be well known.

Several embodiments of the present invention are then specifically shown and described herein. However, it will be recognized that modifications and variations of the present invention will be covered by the foregoing preparation and are within the scope of the appended claims without departing from the scope and intended scope of the invention.