GB2421881A - Adaptive modulation and coding in a personal area network - Google Patents
Adaptive modulation and coding in a personal area network Download PDFInfo
- Publication number
- GB2421881A GB2421881A GB0428459A GB0428459A GB2421881A GB 2421881 A GB2421881 A GB 2421881A GB 0428459 A GB0428459 A GB 0428459A GB 0428459 A GB0428459 A GB 0428459A GB 2421881 A GB2421881 A GB 2421881A
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- data
- modulation
- coding scheme
- packet
- channel quality
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
- H04L1/0026—Transmission of channel quality indication
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
- H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
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- Engineering & Computer Science (AREA)
- Quality & Reliability (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
A method of minimising the effect of a dynamically varying communication channel between a transmitting device and a receiving device in a personal area network using adaptive modulation and coding, the method comprising the steps of: transmitting data to the receiving device over the communication channel using a pre-determined first modulation and coding scheme; receiving the transmitted data at the receiver; determining the quality of the communication channel based on the received data; transmitting the channel quality information to the transmitter; determining at the transmitter, a second modulation and coding scheme associated with the channel quality information received; and transmitting further data using the second modulation and coding scheme.
Description
IMPROVEMENTS IN ADAPTIVE MODULATION AND CODING
The present invention relates to improvements in adaptive modulation and coding (AMC) operation, and in particular to a simplified AMC operation for use in personal area network (PAN) communications.
Link adaptation technology provides a means to cope with the dynamic variation in the quality of a radio communication line, which in turn affects the quality of the signals being received at either the base station or user terminals, or, indeed, any transmitting device or receiving device in a peer-to-peer communication system.
The means of coping with the dynamic channel variation can be realised through the use of various methods and technologies.
Firstly, it is known to adjust the transmission power in an attempt to keep the received signal quality and frame quality constant. For example, the received signal quality is kept constant by making the signal to noise power ratio (SNR) constant. Frame quality is kept constant by making the frame error rate (FER) constant. The purpose of power control is to adapt the transmitter so that the receiver performs in a constant manner. This is desirable in voice communications wherein continuous transmission is a requirement.
Secondly, it is known to use a method known as hybrid automatic repeat request (HARQ). With HARQ, the transmitter resends the packet of data if transmission is not successful. That is, the receiver determines if the packet has been received intact and without any errors by looking at the cyclic redundancy check (CRC) code attached to the packet. If the receiver determines that the packet has been received successfully, an acknowledgement is sent to the transmitter so the transmitter can stop repeatedly sending the packet of data. In this scenario, it is possible that the transmitter uses a different format of coding or modulation with each repeat transmission in an attempt to overcome the dynamic variations in the channel quality.
Thirdly, adaptive modulation and coding (AMC) can be used wherein it is arranged to maximise the data throughput by adaptively changing the modulation and coding scheme. That is, a suitable modulation and coding scheme is selected based on which would be most suitable for the current channel conditions in terms of maximising the throughput.
AMC is implemented in existing standards for packet transmission such as high-speed downlink packet access (HSDPA), HiperLAN/2, IEEE8O2.1 la/i lg/16, 1xEV-DO and 1xEV-DV. AMC is also being considered as one of the key technologies for the future generation of efficient packet data communication systems.
Co-pending application GB 0416522.1 discusses the formation of personal area networks (PAN). In such networks, the coverage area of communications is very small, for example, in the order of 10 to 20 metres.
This is due to the low price of the terminals intended for use within the PAN and the need to limit their consumption of power. Within the PAN, some terminals, which may be either a transmitting device or a receiving device, are expected to move at slow speeds. For example, the terminal speeds may reach up to 3 km/h, i.e. walking speed. This is different to speeds of cellular network terminals, wherein the speed of the terminal could be in excess of 100 km/h. Therefore, the methodology behind the design of communication systems in PAN networks is different to that of cellular networks.
The speed of terminals is closely related to the maximum Doppler spread (fD,max) and the coherence time (Ta) of the communications channel.
Doppler spread is defined as the difference between the highest and the lowest shift in frequency of the received reflections of the carrier frequency. The coherence time is defined as the time over which a communication channel's characteristics stay sufficiently constant in order to successfully transmit a packet of data.
Therefore, the relationship between the terminal speed v(m/s) and the maximum Doppler spread (fb,rnax) can be given as v(m/s) v(m/s).f(I-Jz) JD, rnax= = 2(m) c(m/s) where f(Hz) = carrier frequency and c (=lO8mls) = speed of light.
The approximate relationship between the maximum Doppler spread and the coherence time is given by T= 1 fD, max Therefore, taking an example where the carrier frequency is 5.2 GHz and the terminal speed is 3 km/h, the maximum Doppler spread is given as 14.4 Hz, which corresponds to a coherence time of 69.4 msec. Therefore, if a frame length of packet data is longer than 69.4 msec, channels characteristics may change during the transmission.
On the other hand, if the frame length (in time) for packet data transmission (i.e. the time taken to transmit one packet of data) is much smaller than the coherence time, then it is reasonable to regard the conditions of the transmission channel as being constant for the duration of the transmission of multiple frames of data.
Looking at the frame length of existing standards for packet data transmission, it can be realistically concluded that the channel condition of personal area networks remains almost constant during multiple frame transmission when using these existing standards. For example, in IEEE8O2.1 la, the frame length is 30tsec to 131.2msec. In 1xEV-DO, the frame length is 1.67msec to 26.72msec. In 1xEV-DV, the frame length is 1.25msec to Smsec. Most of these frame lengths are much smaller than 69.4msec, which is the calculated coherence time of a personal area network.
Therefore, it will be shown that AMC operation can be improved in PAN communications by taking into account the slowly varying channel conditions when compared to the frame length (in time) for existing standards.
A conventional closed ioop AMC operation between a base station (BS) / access point (AP) and a mobile station (MS) / access terminal (AT) is shown in the flow diagram of Figure 1.
It will be understood that the procedure shown in Figure 1 is also applicable to peer-to-peer communication systems. For example, the references to the BS/AP and the MS/AT may alternatively indicate a transmitting device and a receiving device respectively.
The AMC operation starts at step S 101. At step S 103, the BS/AP transmits a periodic pilot signal to the MS/AT. The MS/AT receives the periodic pilot signal at step S 105.
At step S 107, the MS/AT carries out a quality measurement procedure on the pilot signal to determine the quality of the transmission channel. The quality measurement may be measured a number of ways. For example, it may be measured using the ratio of power in the carrier signal to the power in the interference signal, known as the carrier to interference ratio (CIR).
Alternatively, it may be measured using the signal to noise plus interference ratio (S1INR), for example. Any other suitable quality measurement techniques may also be used.
Once measured, the quality information is sent back to the BS/AP at step S 109. The B SlAP receives the quality information at step Sill.
Upon receipt of this quality information, the scheduling step occurs at S 113. That is, the BS/AP selects a suitable Modulation Coding Scheme (MCS) level based on the received quality information for the MS/AT associated with that quality information.
The BS/AP transmits data at step Si 15 to the MS/AT over the communication channel using the selected MCS level. The MS/AT receives the data over the communication channel at step S 117. At step S 119, it is determined whether the transmission of all the data packets has been completed. If so, the process ends at step Si 21. Otherwise, the process continues from step S103 again.
It can be seen from this procedure that there are three initial steps before data is transferred between the BS/AP and the MS/AT. That is, the steps of periodic pilot transmission, periodic channel quality measurement and feedback, and scheduling. This results in a significant delay before any data is transferred over the communications channel to the MS/AT.
The present invention aims to overcome or at least alleviate some or all of the aforementioned problems.
In one aspect, the present invention provides a method of minimising the effect of a dynamically varying communication channel between a transmitting device and a receiving device in a personal area network using adaptive modulation and coding, the method comprising the steps of: transmitting data to the receiving device over the communication channel using a pre-determined first modulation and coding scheme; receiving the transmitted data at the receiver; determining the quality of the communication channel based on the received data; transmitting the channel quality information to the transmitter; determining at the transmitter, a second modulation and coding scheme associated with the channel quality information received; and transmitting further data using the second modulation and coding scheme.
In a further aspect, the present invention provides an apparatus comprising a transmitting device and a receiving device, both adapted for use in a personal area network, wherein the transmitting device is arranged to transmit data over a communication channel to the receiving device using a pre-determined first modulation and coding scheme, the receiving device is arranged to receive the data and determine the quality of the communication channel based on the received data, the receiving device further arranged to transmit the channel quality information to the transmitter, the transmitter being further arranged to determine a second modulation and coding scheme associated with the channel quality information received, and also arranged to transmit further data using the second modulation and coding scheme.
In yet a further aspect, the present invention provides a receiving device adapted for use in a personal area network, said receiver arranged to receive data transmitted by a further device using a pre-determined first modulation and coding scheme over a communication channel and to measure the quality of the communication channel using the received data, the receiving device further arranged to transmit information associated with the channel quality to the further device said information suitable for the further device to determine a second modulation and coding scheme to be used for further data to be transmitted.
In yet a further aspect, the present invention provides a transmitting device adapted for use in a personal area network, said transmitting device arranged to transmit data to a further device over a communication channel using a first modulation and coding scheme, and further arranged to determine a second modulation and coding scheme to use based on information received from the further device, said information associated with the channel quality.
The present invention provides the advantage of reducing the overhead in downlink transmissions caused by the transmission of the periodic pilot signal in conventional systems.
Also, the present invention provides the advantage of reducing the overhead in uplink transmissions caused by the transmission of periodic channel quality feedback.
Further, the present invention provides the advantage of reducing the receiving devices' processing overheads due to the periodic measurement of transmission channel quality. This in turn helps to prolong the battery usage of the receiving devices used in the PAN.
A specific embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a flow diagram of a conventional closed loop AMC operation; Figure 2a shows a conventional scheme for signalling channel quality information; Figure 2b shows a scheme for signalling channel quality information according to an embodiment of the present invention; Figure 3 shows a block diagram of an AMC operation according to an embodiment of the present invention.
PREFERRED EMBODIMENT
Referring to Figure 2a, it can be seen that in a conventional AMC operation, the transmitter 201 periodically receives channel quality information 207 from the receiver 203 at all times. This is regardless of when packets of data (205a and 205b) are being transmitted by the transmitter 201.
The PAN used in this embodiment includes a base station (BS) as a transmitting device and a mobile station (MS) as a receiving device.
Referring to Figure 2b, which shows the AMC operation according to this preferred embodiment, it can be seen that channel quality information 219 is only sent back to the transmitter 209 during transmission 217 of data packets (213a and 21 3b). This ensures that uplink and downlink signalling overheads are reduced, as periodic pilot signals are not required and the receiver 211 is not required to send channel quality information 219 at all times.
It can also be seen in Figure 2b that the variation of the channel quality 215 is slow in comparison to the time taken for transmission of channel quality information 219. Therefore, the time 225 between transmission 217 of the initial portion of the data packet 21 3a and the receipt of the feedback 219 on the quality of the communications channel is small compared to the time over which the channel quality varies.
The receiver 211 only sends channel quality information 219 upon receiving data 213a from the transmitter 209. Therefore, the last set of channel quality information 221 is sent when the receiver 211 receives the last portion of the data packet 213a.
The channel quality is measured using any known techniques, for example, the techniques of measuring CIR and S1}R as previously discussed.
The measure of the quality of the channel is carried out using the data signals sent by the transmitter and not a period pilot signal.
At the start of a data packet transmission 217, the transmitter transmits the initial data within the data packet using a pre-determined default MCS level. The pre-determined default MCS level may be set at any level, and must be known to both the transmitting and receiving device. It is preferable to have the MCS level set at a mid point so that the data can still be received successfully without not drastically reducing throughput for a certain range of channel quality. It will be understood that the initial transmission of each data packet may use different pre- determined MCS levels, as will be explained later.
After the initial data within the data packet 213a is transmitted 217, the receiver 211 uses this data to determine the channel quality, as described above. The receiver 211 then sends the channel quality information 219 back to the transmitter 209. The time taken between sending the first portion of the data 217, and the transmitter 209 receiving the channel quality information 219 is depicted in Figure 2b as round trip delay time 225.
After this initial delay time 225, the transmitter 209 uses the received channel quality information 219 to set the MCS level to a level more suited to the measured channel quality and the receiver 211 to which the data is being sent. Therefore, for a time period 227 wherein a further portion of the data packet 213a is transmitted, the MCS level is set at an optimum level according to the channel quality.
After the whole data packet 213a has been transmitted, and the receiver 211 has returned the channel quality information 221, the receiver stops sending any further channel quality information until the transmitter 209 starts to transmit the next data packet 213b. There may be a considerable time delay between the data packet 213a and data packet 213b being transmitted over the PAN, and so the pre-determined MCS level used to transmit the first portion 223 of the data packet 21 3b may not be the same pre- determined MCS level as previously used during the later transmission of the earlier data packet 213a. The reason for this is because the channel conditions are likely to have changed, thus varying the channel quality. In this embodiment, the MCS level used to transmit the first portion 223 of the data packet 21 3b is the same pre-determined MCS level as initially used in the transmission of the data packet 213a.
Referring to Figure 3, the AMC operation according to this embodiment is now explained.
The AMC operation starts at step S301. Next, the base station transmits the data to the mobile station using a fixed level MCS at step S303.
The mobile station detects and receives the data being transmitted by the base station, as shown at step S305.
Upon receipt of this initial data, the mobile station (or receiving device) measures the communication channel quality using the received data at step S307. The measurement of channel quality is carried out using known techniques, as explained above.
The mobile station forwards the channel quality information to the base station at step S309. The base station is then able to use the channel quality information received to select an appropriate MCS level based on this received information and the mobile station, as indicated at step S3 11.
The base station (or transmitting device) transmits the remaining data within the packet, at step S313, using the MCS level selected in step S311.
At step S3 15, the mobile station detects and receives the data. At step S3 17, it is determined whether the whole data packet has been transmitted. If so, the process ends at step S3 19. Otherwise, the process continues from step S305 again.
FURTHER EMBODIMENTS
It will be understood that the embodiment of the present invention described herein is by way of example only, and that various changes and modifications may be made without departing from the scope of the invention.
It will be understood that, although in the embodiment described each initial transmission of a data packet uses the same default predetermined MCS level, the MCS level used may be any other pre-defined MCS level which is determined, for example, by the time when the transmission is occurring, the number of devices within the network, the location of the network or any other relevant parameter that affects the communication channel quality.
It will further be understood that, although the preferred embodiment describes the invention used with a fixed transmitter (base station) and a mobile receiver (mobile station), the transmitters and receivers may be any suitable device capable of transmitting data to, and receiving data from other devices within the personal area network. Any of the transmitters and receivers may be, for example, a mobile computing device such as a mobile telephone, a personal digital assistant (PDA) or such like. Alternatively, any of the transmitters and receivers may be, for example, a fixed device such as a desktop computer, network server, printer, facsimile machine etc. These devices could then be moved at irregular intervals (for example, moved to different offices) and reconnected to a network.
Claims (12)
1. A method of minimising the effect of a dynamically varying communication channel between a transmitting device and a receiving device in a personal area network using adaptive modulation and coding, the method comprising the steps of: transmitting data to the receiving device over the communication channel using a pre-determined first modulation and coding scheme; receiving the transmitted data at the receiver; determining the quality of the communication channel based on the received data; transmitting the channel quality information to the transmitter; determining at the transmitter, a second modulation and coding scheme associated with the channel quality information received; and transmitting further data using the second modulation and coding scheme.
2. The method of claim 1 wherein the data forms the first part of a data packet, and the further data forms the remaining data within that data packet.
3. The method of claim 2, wherein the transmission of channel quality information is stopped after the receiver has received all of the further data within the current data packet.
4. The method of claim 2 further comprising the step of: reverting back to using the pre-determined first modulation and coding scheme at the start of each packet of data being transmitted.
5. The method of claim 2 further comprising the step of: using a further pre-determined modulation and coding scheme at the start of each packet of data being transmitted.
6. Apparatus comprising a transmitting device and a receiving device, both adapted for use in a personal area network, wherein the transmitting device is arranged to transmit data over a communication channel to the receiving device using a pre-determined first modulation and coding scheme, the receiving device is arranged to receive the data and determine the quality of the communication channel based on the received data, the receiving device further arranged to transmit the channel quality information to the transmitter, the transmitter being further arranged to determine a second modulation and coding scheme associated with the channel quality information received, and also arranged to transmit further data using the second modulation and coding scheme.
7. The apparatus of claim 6 wherein the data forms the first part of a first data packet, and the further data forms the remaining data within that data packet.
8. The apparatus of claim 7 wherein the transmitter is arranged to stop the transmission of channel quality information after the receiver has received all of the further data within the current data packet.
9. The apparatus of claim 7 wherein the pre-determined first modulation and coding scheme is used at the start of each packet of data being transmitted.
10. The apparatus of claim 7, wherein a further pre-determined modulation and coding scheme is used at the start of each packet of data being transmitted.
11. A receiving device adapted for use in a personal area network, said receiver arranged to receive data transmitted by a further device using a pre-determined first modulation and coding scheme over a communication channel and to measure the quality of the communication channel using the received data, the receiving device further arranged to transmit information associated with the channel quality to the further device said information suitable for the further device to determine a second modulation and coding scheme to be used for further data to be transmitted.
12. A transmitting device adapted for use in a personal area network, said transmitting device arranged to transmit data to a further device over a communication channel using a first modulation and coding scheme, and further arranged to determine a second modulation and coding scheme to use based on information received from the further device, said information associated with the channel quality.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0428459A GB2421881A (en) | 2004-12-29 | 2004-12-29 | Adaptive modulation and coding in a personal area network |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0428459A GB2421881A (en) | 2004-12-29 | 2004-12-29 | Adaptive modulation and coding in a personal area network |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0428459D0 GB0428459D0 (en) | 2005-02-02 |
| GB2421881A true GB2421881A (en) | 2006-07-05 |
Family
ID=34130997
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0428459A Withdrawn GB2421881A (en) | 2004-12-29 | 2004-12-29 | Adaptive modulation and coding in a personal area network |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2421881A (en) |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5764699A (en) * | 1994-03-31 | 1998-06-09 | Motorola, Inc. | Method and apparatus for providing adaptive modulation in a radio communication system |
| WO2001099384A2 (en) * | 2000-06-20 | 2001-12-27 | Telefonaktiebolaget Lm Ericsson (Publ) | Method and apparatus for dynamic packet selection in bluetoth |
| US20030123598A1 (en) * | 2001-12-28 | 2003-07-03 | Sridhar Gollamudi | Multi-channel adapative quality control loop for link rate adaptation in data packet communications |
| GB2385754A (en) * | 2002-02-25 | 2003-08-27 | Toshiba Res Europ Ltd | Selection of modulation scheme using information in a message returned from receiver to transmitter |
| EP1475898A1 (en) * | 2003-05-03 | 2004-11-10 | Samsung Electronics Co., Ltd. | Method and apparatus for ultra wideband wireless communication using channel information |
-
2004
- 2004-12-29 GB GB0428459A patent/GB2421881A/en not_active Withdrawn
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5764699A (en) * | 1994-03-31 | 1998-06-09 | Motorola, Inc. | Method and apparatus for providing adaptive modulation in a radio communication system |
| WO2001099384A2 (en) * | 2000-06-20 | 2001-12-27 | Telefonaktiebolaget Lm Ericsson (Publ) | Method and apparatus for dynamic packet selection in bluetoth |
| US20030123598A1 (en) * | 2001-12-28 | 2003-07-03 | Sridhar Gollamudi | Multi-channel adapative quality control loop for link rate adaptation in data packet communications |
| GB2385754A (en) * | 2002-02-25 | 2003-08-27 | Toshiba Res Europ Ltd | Selection of modulation scheme using information in a message returned from receiver to transmitter |
| EP1475898A1 (en) * | 2003-05-03 | 2004-11-10 | Samsung Electronics Co., Ltd. | Method and apparatus for ultra wideband wireless communication using channel information |
Non-Patent Citations (2)
| Title |
|---|
| Cepeda, R. et al., IEEE 55th Vehicular Technology Conference, published 2002, pp1497-1501, vol. 3, "The performance of robust adaptive modulation over wireless channels with non reciprocal interference" * |
| Yoon, J-H. et al., IEEE Wireless Communications and Networking Conference, published 2004, IEEE, pp1014-1017, vol. 2, "Packet and modulation type selection scheme based on channel quality estimation for Bluetooth evolution systems" * |
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| Publication number | Publication date |
|---|---|
| GB0428459D0 (en) | 2005-02-02 |
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