WO2009102190A2

WO2009102190A2 - Dynamic harq with adaptive power control for wireless transmission

Info

Publication number: WO2009102190A2
Application number: PCT/MY2009/000029
Authority: WO
Inventors: Rashid Abdelhaleem Saeed; Chee Kyun Ng; Hafizal Mohamad; Borhanuddin Mohamad Ali
Original assignee: Mimos Berhad
Priority date: 2008-02-14
Filing date: 2009-02-13
Publication date: 2009-08-20
Also published as: MY151716A; WO2009102190A3

Abstract

In a specific embodiment, our method of communicating a message between a transmitting station and a receiving station may be outlined as employing a hybrid automated retransmission request (HARQ) protocol in a multihop relay network. Our method includes the steps of, upon detecting transmission errors, obtaining a signal-to- interference and noise ratio (SINR) measurement at the physical layer (PHY) of the data transport framework from a forwarding Relay Station (RS2) by a Mobile Station wherein the estimates of the mean or standard deviation of the SINR measurement may be derived and updated. The derived values to be compared against a Bit Error Rate (BER) value as a channel quality threshold parameter, wherein channel quality is deemed good if the error function value is at least a BER threshold and normal HARQ encoding follows. Channel quality is deemed bad if the error function value is less than the BER threshold. Channel quality information is reported via at least one of a Channel Quality Information Channel (CQICH) or channel measure report response (REP-RSP) messaging. Transmission power control information is then encoded into a hybrid automated retransmission request (HARQ+) then transmitted.

Description

Dynamic HARQ with adaptive power control for wireless transmission

TECHNICAL FIELD

[001] This invention concerns a method or protocol for transmission of data between a transmitting station and a receiving station. In particular, it concerns a method of error detecting coded data block transmitted and correcting the error via automated repeat request (ARQ), including hybrid ARQ (HARQ), such as that for wireless transmission according to IEEE 802.16 standards for WiMAX.

BACKGROUND ART

[002] In data transmission methods or protocols, automated repeat request (ARQ) is used as an error control method involving acknowledgements and timouts in order to ensure data frame transmission reliability. If an acknowledgement is not received before the timeout, the sender usually retransmits the data frame or block. Error- detection (ED) information bits (such as cyclic redundancy check, CRC) are added to the data block.

[003] A variation of ARQ is the more complex Hybrid ARQ (HARQ) protocol which provides better performance for wireless channels. In HARQ, in addition to the ED, forward error correction (FEC) bits, such as Reed-Solomon code or Turbo code, are also added. Hence, HARQ performs better than ARQ in poor signal conditions but results in lower throughput in good signal conditions in which the basic ARQ is better. The simplest version of HARQ, Type I HARQ, adds both ED and FEC information to each message prior to transmission. When the coded data block is received, the receiver first decodes the error-correction code. If the channel quality is good enough, all transmission errors should be correctable, and the receiver can obtain the correct data block. If the channel quality is bad and not all transmission errors can be corrected, the receiver will detect this situation using the error-detection code, then the received coded data block is discarded and retransmission is requested by the receiver, similar to ARQ. [004] Type II HARQ transmits only ED bits or only FEC information and ED bits on a given transmission, typically alternating on successive transmissions. It is well known in the art that, Type II HARQ avoids the capacity loss suffered by Type I HARQ by having the FEC bits transmitted as needed on subsequent retransmission rather than on the first transmission, thus achieving the performance of basic ARQ under good channel quality conditions. It is also known that erroneously received coded data blocks are often stored at the receiver rather than discarded, and when the retransmitted block is received, the two blocks are combined using Chase combining method to increase the probability of successful decoding.

[005] Various approaches have been taken to provide dynamic or adaptive control of resources in a framework that is integrated with HARQ, as well as to provide a better quality of service (QoS) information. For example, in U.S. Patent No. 7,155,655 (TelefonAB LM Ericsson), it is disclosed an adaptive HARQ protocol that includes variables based on signal to noise ratio (SNR) of the communication channel. The transmission variables include the ratio of initial transmission SNR (SNR₁) to retransmission SNR (SNR₂), i.e. SNR₁ZSNR₂ as a performance indicator which is used to variably encode the retransmission request. There is no reference to dynamically control transmission power, however.

[006] In U.S. Patent No. 6,308,294 (Motorola) discloses an adaptive HARQ protocol using turbo encoding wherein self-decodable blocks, other than the first block, allow retransmissions of different sizes and which may improve upon transmission in fading channels. This includes turbo code and convolutional code which may involve redundancy selection, including incremental redundancy. It does not involve channel quality feedback or power control features in the encoding the retransmission request. U.S. Patent No. 6,744,766 (MeshNetworks) proposed a retransmission protocol whereby failed segments are retransmitted multiple times per MAC transaction without any power control feature or channel quality indication.

[007] In U.S. Patent No. 7,096,401 (Motorola) teaches a method which increases the likelihood of a correct decoding on later transmission by comparing the previous bits received and current bits received. U.S. Patent No. 7,002,923 (Matsushita) provides a channel quality measurement for HARQ encoding by counting the decoded error (NAK) messages and obtaining average number of retransmissions per data unit, or the average number of retransmissions per code word.

[008] In U.S. Patent No. 7,000,174 (Research in Motion) references have been made in respect of systems without a feedback channel, the performance may be defined by the bit error rate (BER) as a probability of a transmitted bit would be decoded erroneously by the receiver. Although it is known that BER would decrease and performance improves with higher transmitted signal power, conserving power is always a concern particular for mobile terminals. Thus, techniques such as FEC are used to improve BER without increasing power or achieving an acceptable BER with less power. While the HARQ protocol of this prior art uses code puncturing with Turbo and low density parity check (LDPC) codes, there is also mentioned the use of signal- to-noise (SNR) as a signal quality measurement at the receiver or on a desired QoS to determine the amount of puncturing.

[009] A method of controlling transmission of retransmission data using a traffic-to- pilot power ratio (TPR) included in the retransmission control signal is disclosed in U.S. Patent No. 7,200,789 (Samsung) wherein it is known that transmission power control feature is included in the retransmission request of CDMA2000 or 3 G systems in the form of TPR according to predetermined rates and which is not adaptive. There is also mention in this prior art of interference being considered in the form of a ratio Eb/Nt (energy to interference per bit) to avoid problems that might arise as a result of variable power. If the retransmission power is higher than the required power, the retransmission power functions as interference to other users, deteriorating a channel environment. If the retransmission power is lower than required power, HARQ performance deteriorates undesirably. Another problem arising from variable power is that the same code symbols as those transmitted at initial transmission are transmitted during retransmission, so performance improvement through incremental redundancy (IR) becomes impossible. [010] U.S. Patent No. 7,206,598 (Qualcomm) disclosed an apparatus and a method for a control channel power allocation in a communication system at the medium access control (MAC) level. However, the power control is not adaptive and appears to be in an order of increasing required MAC channel power to an order of decreasing forward link signal to interference and noise ratio (FL S INR). The set of parameters may include signal-to-interference and noise ratio (SESfR) measurements and BER.

[011] U.S. Patent No. 7,257,423 (Matsushita) discloses a base station with transmission assignment control method whereby a transmission power determiner monitors transmission power resources and determines the transmission power of a high-speed physical downlink shared channel (HS-PDSCH) and the transmission power of a pilot channel. The signal-to-interference ratio (SIR) of the HS-PDSCH is estimated based on the channel quality indicator (CQI) signal and transmission power. With this prior art method, it is possible to maximise throughput in consideration of the transmission power of the HS-PDSCH. However, the transmission power control method disclosed is not adaptive and appears to follow a schedule for maximizing throughput by determining the transmission power of HS-PDSCH whereby its modulation scheme is according to CQI.

SUMMARY OF DISCLOSURE

[012] To achieve better conservation of resources, particularly transmission power so that low power devices may be used in the proposed network, and to increase data throughput, we have now proposed in the following a dynamic HARQ protocol whereby normal HARQ protocol is use for good channel quality but when poor channel quality or erroneous decoding of transmission occurs, a method of encoding retransmission power information into the HARQ is provided so that the channel quality may be adaptively and dynamically maintained.

[013] In a specific and preferred embodiment, our method of communicating a message between a transmitting station and a receiving station may be outlined as employing a hybrid automated retransmission request (HARQ) protocol in a multihop relay network, wherein said method including the steps of, upon detecting transmission errors, (a) obtaining a signal-to-interference and noise ratio (SINR) measurement at the physical layer (PHY) of the data transport framework from a forwarding Relay Station (RS2) by a Mobile Station wherein: (i) the estimates of the mean or standard deviation of the SINR measurement may be derived and updated; (ii) using such derived values to be compared against a Bit Error Rate (BER) value as a channel quality threshold parameter, wherein: channel quality is deemed good if the error function value is at least a BER threshold and normal HARQ encoding follows; channel quality is deemed bad if the error function value is less than the BER threshold;

(iii) reporting channel quality information via at least one of a Channel Quality Information Channel (CQICH) or channel measure report response (REP-RSP) messaging;

(b) encoding transmission power control information into a hybrid automated retransmission request (HARQ+) wherein said power control information is calculated from:

P (k + l) = — £ P (k) (A)

SINR(K) wherein P(k) is the transmitter power of the i'^h link in the k'^h transmission

(iteration), and each burst measures individually its current SINR and tries to achieve its target γ] in the next transmission, by increasing its power when current SINR is below its target γ] and vice versa.

(c) transmitting said hybrid automated retransmission request with power control information (HARQ+).

[014] Other alternative embodiments or configurations of our method are further described in the Detailed Description that follows: LIST OF ACCOMPANYING DRAWINGS

[015] For a better understanding of our invention, references shall now be made to the following drawings and the accompanying detailed description below wherein specific or preferred embodiments as exemplary and non-limiting illustrations of our invention are described, in which:

[016] FIGURE 1 (Prior Art) describes a schematic example of configuration of a plurality of Base Stations, Relaying Stations and Mobile Stations in a mesh topology such as that prescribed in IEEE 802.16) standard which is also known as WiMAX;

[017] FIGURE 2 (Prior Art) depicts a schematic diagram showing interferences between adjacent Base Stations, Relay Stations and Mobile Stations that typically occurs in existing deployment;

[018] FIGURE 3 illustrates a logic flow diagram outlining the algorithm of the dynamic HARQ according to our invention as an improvement over the prior art; and

[019] FIGURE 4 shows a schematic diagram of the hardware aspect of our invention in terms of the physical (PHY) and media access control (MAC) layers comprised in the proposed dynamic HARQ; and

[020] FIGURE 5 depicts a model or example of a transmitter - receiver configuration which may enable communications according to our invention. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[021] Although in the following detailed description our invention is described in respect of implementation in a HARQ protocol, it is not necessarily limited to such wireless retransmission operation because, in a broad sense, our invention comprises a method of communicating a message comprising a coded data block with error detection information, i.e. any error detection information, which is channelled between a transmitting station and a receiving station. Generally, our method comprises the steps of determining channel quality by attempting to decode said data block with error- correction code included with said error detection information whereby channel quality is deemed good when all transmission errors are corrected and said receiving station accepts said data block; and channel quality is deemed bad when not all transmission errors are corrected and requests for retransmission.

[022] The receiving station may discard the data block from the received packets and buffer the deleted block for chase combining with the retransmitted block. As such, our method may include certain elements of error detection coding of conventional ARQ in combination with forward error code (FEC) used in HARQ, wherein error detection coding such as cyclic redundancy (CRC), or error correction coding such as any one of Reed-Solomon code or Turbo code are employed.

[023] While conventional HARQ protocol will be implemented when the channel quality is good, our invention will come into play in determining channel quality based on our own measurements of thresholds and upon encountering bad channel quality, calculate and encode the requisite transmission power control information into the retransmission request which includes the HARQ protocol. Preferably, the channel quality parameter is provided as a fast response or feedback channel such as a Channel Quality Information Channel (CQICH). The frame of our proposed CQICH may follow that as prescribed in the IEEE 802.16 standard.

[024] For purposes of measuring channel quality, signal to interference and noise ratio (SINR) measurements are obtained and used as a channel quality parameter. The interferences that may occur is shown schematically in FIGURE 2. The SINR may be taken and calculations performed at preferably one of the Relay Stations (RS). For ease of implementation, the SINR measurement may be specified to be taken mandatorily at the forwarding Relay Station (RS2) for ease of subsequent calculation and threshold comparison prior to encoding the requisite adaptive retransmission power information.

[025] Once the SINR measurement is obtained, it may be sent to or acquired by a Mobile Station (MS) for purposes of reporting transmission channel quality. The Mobile Station (MS) may then derive and/or update the estimates of the mean or standard deviation of the acquired SINR measurements and report the measurement via a CQICH and/or channel measure Report-Response (REP-RSP) messaging. Specifically, the SINR measurement may be used to calculate a channel quality value to be compared against a channel quality threshold parameter. In the comparison step, upon determining from a relationship that the channel quality value is below a threshold, transmission power control information may then be encoded into the retransmission request. Specifically, the SINR may be measured as the physical (PHY) layer of the data transport framework according to the following relationship:

wherein P is the transmitted power level per a subcarrier for the current transmission, including MS Tx antenna gain; L is the estimated average current link propagation loss, L = d" where d" is the distance from MS in cell i using link / to its BS/RS and n is the propagation constant, ranging typically in value from 2 to 4; ^ (N + 1) is the estimated average power level of the noise and interference per a subcarrier at BS; R is the number of repetitions for the modulation/FEC (frame error check) rate;

MS₀S is the correction term for MS specific power offset with initial zero is zero, and

BS₀S is the correction term for MS-specific power offset. [026] Alternatively, the SINR measurement is used in a channel quality relationship in the form of a complementary error function (erfc) which value is compared against a threshold value comprising a bit error rate (BER) in the following relationship

-erfcl . ^l \ < BER .... (2)

2 [yfsΪNR J wherein channel quality is deemed bad if the error function value is less than the BER threshold and the requisite transmission power control information is encoded into the retransmission request. In our method, the channel quality is maintained by seeking to keep each SINR measured in the relationship to a value above a required BER threshold according to the following relationship:

SINR₁ = Y^ y₀ , X ≤ i ≤ M .... (3)

[027] The transmission power control information may be calculated from the following relationship, i.e.

P (k + \) = —^ P (A:) .... (4)

SINR(k) wherein P(k) is the transmitter power of the i'^h link in the k ^th transmission (iteration), and each burst measures individually its current SINR and tries to achieve its target γ] in the next transmission, by increasing its power when current SINR is below its target γ] and vice versa.

[028] Finally, the power control message is encoded to be sent as HARQ+ (i.e. dynamic HARQ modified with adaptively encoded power control message and sent through a closed loop power control messaging channel which may preferably be in accordance with the IEEE 802.16 prescribed standard.

[029] An exemplary configuration of a transceiving system implementing the dynamic HARQ protocol supported by power control according to our method is shown in FIGURE 5. At the transmitter, a block of information bits are encoded and stored. Next, the combined H-ARQ/power control algorithm adjusts the SNR for the modulation constellation level for each transmission. The receiver estimates the channel characteristics and, based on the BER appeared in the demodulation constellation, the feedback controller sends back the CQICH message.

[030] Our adaptive and dynamic HARQ protocol which method is as outlined above may be implemented in various wireless networks, particularly in a multihop relay network, including wireless mesh, grids, network remote station repeaters and like configurations which can extend networks and connect to backhaul. A person skilled in the art will be able to determine the configuration, layout and type of equipment required for implementing our aforesaid method, including choice or models of transceivers required.

[031] While our invention may be advantageously implemented in a wide variety of wireless network transmission protocols, it will be particularly suitable for wireless wide area network (WirelessWAN), metropolitan area network (WirelessMAN) or otherwise based on IEEE 802.16 standard which is also known to the industry as WiMAX. It will be obvious to a skilled person to make modifications, variations or substitution of any steps, stages or formulaic relationship of parameters to our invention as disclosed above while retaining our basic working principles or concepts. These modifications are to be regarded as falling within the scope and letter of our invention as defined in the following claims.

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Claims

CLAIMSWhat we claim as novel is:

1. A method of communicating a message comprising a coded data block with error detection information channelled between a transmitting station and a receiving station, said method comprising: (a) determining channel quality by attempting to decode said data block with error- correction code included with said error detection information whereby (i) channel quality is deemed good when all transmission errors are corrected and said receiving station accepts said data block; (ii) channel quality is deemed bad when not all transmission errors are corrected and requests for retransmission; whereupon encountering a bad channel quality, said retransmission request includes:

(b) obtaining a signal-to-interference and noise ratio (SINR) measurement and including said SINR as a channel quality parameter;

(c) encoding transmission power control information into said request for retransmission;

(d) transmitting said retransmission request.

2. A method of communicating a message according to Claim 1 wherein the retransmission request comprises an automated retransmission request (ARQ) protocol or derivations therefrom including hybrid ARQ (HARQ).

3. A method of communicating a message according to Claim 1 wherein the error- detection code includes combining forward error code (FEC) and hybrid ARQ by encoding the data block plus error detection information with an error correction code.

4. A method of communicating a message according to Claim 3 wherein the error detection information includes any one of cyclic redundancy check (CRC) functions and the error correction code includes any one of Reed-Solomon code or Turbo code.

5. A method of communicating a message according to Claim 1 wherein the channel quality parameter is provided as a fast feedback channel, including as a Channel Quality Information Channel (CQICH).

6. A method of communicating a message according to Claim 5 wherein SINR measurement is performed at least a Relay Station (RS).

7. A method of communicating a message according to Claim 6 wherein the SINR measurement is performed mandatory at the forwarding Relay Station (RS2).

8. A method of communicating a message according to Claim 6 wherein the SINR measurement is acquired by a Mobile Station (MS) for purposes of reporting transmission channel quality.

9. A method of communicating a message according to Claim 8 wherein the

Mobile Station (MS) derives and/or updates estimates of the mean or standard deviation of the acquired SINR measurement.

10. A method of communicating a message according to Claim 8 wherein the SINR measurement is reported via at least one of CQICH and/or channel measure Report- Response (REP-RSP) messaging.

11. A method of communicating a message according to Claim 1 wherein the SINR measurement is used to calculate a channel quality value to be compared against a channel quality threshold parameter.

12. A method of communicating a message according to Claim 11 wherein upon determining the channel quality relationship value is below the threshold, transmission power control information is encoded into the retransmission request.

13. A method of communicating a message according to Claim 1 wherein the SINR is measured at the physical layer (PHY) of the data transport framework according to the following relationship:

wherein P is the transmitted power level per a subcarrier for the current transmission, including MS Tx antenna gain; L is the estimated average current link propagation loss, L = d" where d" is the distance from MS in cell / using link / to its BS/RS and n is the propagation constant, ranging typically in value from 2 to 4; ∑(N + 1) is the estimated average power level of the noise and interference per a subcarrier at BS;

R is the number of repetitions for the modulation/FEC (frame error check) rate;

MS_0S is the correction term for MS specific power offset with initial zero is zero, and BS₀₅ is the correction term for MS-specific power offset.

14. A method of communicating a message according to Claim 1 wherein the SINR measurement is used in a channel quality relationship in the form of a complementary error function (erfc) which value is compared against a threshold value comprising a bit error rate (BER) in the following relationship

wherein channel quality is deemed bad if the error function value is less than the BER threshold and the requisite transmission power control information is encoded into the retransmission request.

15. A method of communicating a message according to Claim 14 wherein channel quality is maintained by seeking to keep each SINR measured in the relationship to a value above a required BER threshold according to the following relationship:

SINR₁ = y, ≥ r₀, X ≤ i ≤ M .... (3)

16. A method of communicating a message according to Claim 1 wherein the transmission power control information is calculated from:

P (k + \) = — r -^τ P {k) .... (4)

SINR(k) wherein P(k) is the transmitter power of the i'^h link in the k ^lh transmission (iteration), and each burst measures individually its current SINR and tries to achieve its target γ] in the next transmission, by increasing its power when current SINR is below its target γ] and vice versa.

17. A method of communicating a message between a transmitting station and a receiving station employing a hybrid automated retransmission request (HARQ) protocol in a multihop relay network, said method including the steps of, upon detecting transmission errors,

(a) obtaining a signal-to-interference and noise ratio (SINR) measurement at the physical layer (PHY) of the data transport framework from a forwarding Relay Station (RS2) by a Mobile Station wherein:

(i) the estimates of the mean or standard deviation of the SINR measurement may be derived and updated;

(ii) using such derived values to be compared against a Bit Error Rate (BER) value as a channel quality threshold parameter, wherein: channel quality is deemed good if the error function value is at least a BER threshold and normal HARQ encoding follows; channel quality is deemed bad if the error function value is less than the BER threshold; (iii) reporting channel quality information via at least one of a Channel

Quality Information Channel (CQICH) or channel measure report response (REP-RSP) messaging;

P (k + \) = — £ P (k) (4)

SINR(k) wherein P(Jk) is the transmitter power of the i^th link in the k'^h transmission (iteration), and each burst measures individually its current SINR and tries to achieve its target γ] in the next transmission, by increasing its power when current SINR is below its target γ] and vice versa.

18. A method of communicating a message according to Claim 1 implemented in a multihop relay network, including wireless mesh, grids, network remote station repeaters and like configurations which can extend networks and connect to backhaul.

19. A plurality of transmitting and receiving devices capable of being configured to implement at least one of the methods according to Claims 1 - 18.

20. A transceiver configured to operate complementarily in a network implementing at least one of the methods according to Claims 1 - 18.

21. A wireless broadband telecommunications network employing any one of the methods according to Claims 1 — 18, including any one of wireless wide area network (WirelessWAN), metropolitan area network (WirelessMAN) or based on IEEE 802.16 standard (WiMAX).

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