HK1121621A - Method and apparatus for selecting transmission modulation rates in wireless devices for a/v streaming applications - Google Patents

Description

Method and apparatus for selecting a transmit modulation rate for an A/V streaming application in a wireless device

Cross reference to related applications

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Statement regarding federally sponsored research or development

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Reference material submitted on optical disc

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Copyright notice

Some of the material in this patent document is subject to copyright protection by copyright laws in the united states and other countries. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the U.S. patent and trademark office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive his rights to secure this patent document, including not restricting his rights to 37 c.f.r. § 1.14.

Technical Field

The present invention relates generally to wireless communications, and more particularly to streaming applications for wireless devices, and most particularly to selecting modulation rates in wireless systems to optimize real-time or a/V streaming.

Background

Wireless communication has proliferated in the last few years. The basic feature of wireless communication is to send and receive a modulated RF carrier signal carrying information over the air (without wires) between a transmitter and a receiver. Various modulation techniques are used. The robustness of these modulation techniques varies. In general, more robust techniques have lower transmission rates but produce fewer errors, while less robust techniques transmit at higher rates but produce more errors.

One particular type of wireless communication system is a Wireless Local Area Network (WLAN). WLANs are established in accordance with a number of standards, particularly several 802.11x IEEE standards. The information is typically transmitted as packets that include identification information, actual information, and error information. The complete message may be included in many different packets.

In 802.11x WLANs (and many types of wireless systems), it is often necessary to determine the maximum data rate at which a transmission may occur from a transmitter to a receiver. The selection of the maximum data rate is necessary to maximize the utilization of resources and to serve as many customers as possible. In 802.11x WLANs, the selection of the transmission data rate is typically adaptively based on the Packet Error Rate (PER).

The adaptive prior art method is shown in the flow chart of fig. 1. The transmission of data packets is initiated at a certain data rate, typically the maximum data rate. Transmitting at the selected rate (initially the maximum rate). The transmitted packet is received and the PER is measured. The transmission rate is adjusted based on the PER and transmission continues at the new rate. The process continues and the rate is adjusted (up or down) as more packets are sent and received.

For example, the maximum data rate (corresponding to the most complex modulation) may initially be 54Mbps, which corresponds to 64QAM modulation. If more than three transmission errors occur sequentially at the data rate, the data rate may be reduced to 48Mbps, and if three transmission errors occur sequentially at 48Mbps, the transmission data rate is reduced to 36Mbps (16 QAM), which is a more robust but less efficient modulation scheme. If more than ten packets are successfully transmitted at 36Mbps, the data rate may be increased to 48 Mbps.

The above scheme works well for data-centric applications such as web browsing or email synchronization. The adaptive rate selection mechanism is aggressive in maximizing the data rate, but it does so by causing packet transmission errors, and it uses these transmission errors to estimate the performance limit. These transmission errors can be reduced if the parameters are carefully selected, and the data transfer is acceptably reliable and fast if combined with 802.11x retransmissions.

Problems can arise for high throughput and real-time applications where packet errors can cause packets to be received too late to be useful, or where packet error rates (and subsequently delays caused by retransmissions) cause transmit data buffers to overflow. In addition, the aggressive schemes described above result in frequent fluctuations in the transmission data rate, which may affect the video quality in a/V streaming applications being viewed, for example, where the transmitted video is transrated to match the available 802.11x bandwidth. In such applications, it is desirable to minimize the number of packet transmission errors. A simple scheme is to simply transmit at the lowest data rate (simplest modulation), for example 6Mbps for 802.11 a. However, this is generally unacceptable because it makes very inefficient use of the wireless medium. The purpose of the algorithm for selecting the transmission rate for real-time or a/V streaming applications over a wireless link should therefore be to select a modulation that maximizes the transmission data rate while avoiding any packet errors and at the same time reducing fluctuations in the data rate.

Disclosure of Invention

One aspect of the present invention is a method and apparatus for determining a transmission rate in a wireless communication system by: initiating transmission at an initial data rate; transmitting data packets at a selected rate that is initially the initial rate; receiving the transmitted data packet; measuring at least one of a signal to noise ratio (SNR) or a signal to interference and noise ratio (SINR) to produce a measured SNR/SINR signal; and adjusting the transmission rate based on the measured SNR/SINR signal and information about Packet Error Rate (PER) as a function of SNR/SINR.

The invention has particular application to data streaming applications and may be implemented in a Wireless Local Area Network (WLAN). The present invention adjusts the transmission rate to a maximum value while avoiding packet errors without measuring PER. Headroom may be subtracted from the measured SNR/SINR and the modified value used to determine the transmission rate. The average SNR/SINR value may also be used.

Another aspect of the present invention is a wireless communication system apparatus, comprising: a transmitter for transmitting data packets at the selected rate and having a transmission rate control section which adjusts the transmission rate based on the measured SNR/SINR and information on Packet Error Rate (PER) as a function of SNR/SINR; and a receiver for receiving the transmitted data packets and having SNR/SINR detection means for detecting at least one of a signal to noise ratio (SNR) and a signal to interference and noise ratio (SINR) of the received data packets to produce a measured SNR/SINR signal.

Another aspect of the present invention is a wireless communication system apparatus, comprising: means for transmitting data packets at the selected rate; means for receiving the transmitted data packet; means for measuring at least one of a signal to noise ratio (SNR) or a signal to interference and noise ratio (SINR) of the received data packets to produce a measured SNR/SINR signal; and means for adjusting the transmission rate based on the measured SNR/SINR signal and information on Packet Error Rate (PER) as a function of SNR/SINR.

Additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The present invention will be more fully understood by reference to the accompanying drawings, which are for illustrative purposes only:

fig. 1 is a flow chart of a prior art adaptive rate selection method.

Fig. 2 is a flow chart of a rate selection method of the present invention.

Fig. 3 is a schematic diagram of a wireless communication device implementing the present invention.

Fig. 4 is a flow chart of an additional feature of the present invention of using headroom in rate determination.

Fig. 5 is a schematic diagram of an additional feature of the present invention of using headroom in rate determination.

Fig. 6 is a flow diagram of an additional feature of the present invention of using an average SINR value in rate determination.

Fig. 7 is a diagram illustrating additional features of the present invention for using an average SINR value in rate determination.

Fig. 8 is a flow chart of another embodiment of a rate selection method according to the present invention.

Detailed Description

Referring more specifically to the drawings, for illustrative purposes, the present invention is embodied in the methods and apparatus generally shown in fig. 2-8. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the specific steps and sequence of the method may be varied without departing from the basic concepts as disclosed herein.

The rate selection method of the present invention is illustrated in the flow chart of fig. 2. The transmission of data packets is initiated at a certain data rate, typically the lowest data rate, as shown in step 10. At step 11, transmission is performed at the selected rate (initially the lowest rate). The transmitted packet is received in step 12 and the SNR/SINR (signal to noise ratio or signal to interference and noise ratio or both) is measured in step 13. Based on the measured SNR/SINR and information about PER (packet error rate) as a function of SNR/SINR (as will be explained further below), the transmission rate is adjusted, step 14, and transmission continues at the new rate, step 11. The process continues and as more packets are sent and received, the rate is adjusted (up or down)

Fig. 3 shows a wireless communication device 20, which comprises a Transmitter (TX)21 and a Receiver (RX) 22. Because transmitter 21 may also receive data and receiver 22 may also transmit data, they are both "transceivers" in a more general sense, but in the illustrative wireless system 20, the primary function of TX21 is to transmit data to RX22, and the primary function of RX22 is to receive data from TX21, e.g., TX21 is a base station and RX22 is a remote station. The transmitter 21 includes a modulation and transmission (mod/TX) component 23 connected to an antenna (ANT1)24, and also includes a reception and demodulation (RX/demod) component 25 also connected to the antenna 24. The receiver 22 comprises a receiving and demodulating part 26 connected to an antenna (ANT2)27, and also a modulating and transmitting part 28 also connected to the antenna 27. Because these components are the basic components of a wireless system, are well known in the art, and can be implemented in many different embodiments and configurations, they are shown in a general functional representation. The invention does not depend on the specific physical implementation, configuration or embodiment thereof.

TX21 further comprises a TX rate control section 30 and a retransmission control section 31, both of which are connected to modulation/transmission section 23. The TX rate control section 30 controls the rate at which the mod/TX section 23 transmits data. The retransmission control section 31 controls retransmission by the TX21 of a packet received in error at the RX 22. RX22 further comprises SNR/SINR detection means 32 and error detection means 33, both of which are connected to reception/demodulation means 26. SNR/SINR detection component 32 measures the signal-to-noise ratio (SNR) or Received Signal Strength Indicator (RSSI) of the received signal at RX22 and preferably also the signal-to-interference-and-noise ratio (SINR) of the signal. Any one or more of these three parameters (SNR, RSSI, SINR) may be measured and used to implement the present invention, although ideally these three values are used. The measured value will generally be referred to as SNR/SINR. Error detection component 33 measures errors in packets received at RX22 and also measures the Packet Error Rate (PER). Error detection is necessary so that erroneous or lost packets can be retransmitted.

In operation, in wireless system 20, TX21 transmits data packets from ANT1 to ANT2 at RX 22. If an error is detected in the received packet, error detection component 33 will typically discard the packet and, in addition, an ACK packet will not be sent back to TX21 for the received packet (or for a group of received packets that includes the packet, as is done in some communication protocols). The absence of an ACK packet will cause a retransmission from TX 21. The process of generating a retransmission of a packet is represented by the retransmission (RE-TX) signal in fig. 3.

Also in operation of the wireless system 20, in accordance with the invention, the SNR/SINR detection block 32 measures the SNR and/or SINR of received data packets and sends an SNR/SINR signal back to the RX/demod block 25 via the mod/TX block 28, which RX/demod block 25 inputs into the TX rate control block 30. TX rate control section 30 uses the SNR/SINR data in combination with information about PER as a function of SNR/SINR (discussed further below) to determine an optimal transmission rate and thereby control the rate of modulation/transmission of data packets.

Information may be transmitted over a wireless channel by any of a variety of transmission modes (i.e., particular modulation types and rates). The present invention does not require any particular transmission mode. The invention applies to wireless systems operating in any transmission mode suitable for the application. Thus, the wireless system 20 may operate with various levels of QAM (quadrature amplitude modulation), including 4QAM, 16 QAM, 64QAM, and 256 QAM (also known as X-level QAM or QAM-X), but may also operate in other modes, including BPSK, QPSK, PSK, GMSK, and FSK.

The present invention applies to 802.11x Wireless Local Area Networks (WLANs), and to many other types of wireless systems. The present invention is directed to determining the maximum data rate at which transmission may occur from a transmitter to a receiver. The selection of the maximum data rate is necessary to maximize the utilization of resources and to serve as many customers as possible.

The invention has particular application to high throughput and real-time applications where packet errors may cause packets to be received too late to be useful, or where packet error rates (and subsequently delays caused by retransmissions) cause the transmit data buffer to overflow. One particular application of the invention is, for example, an a/V (audio video or audiovisual signal) streaming application where the transmitted video is transrated to match the available 802.11x bandwidth. In such applications, it is desirable to minimize the number of packet transmission errors, but simply transmitting at the lowest data rate (simplest modulation), such as 6Mbps for 802.11a, is generally unacceptable because it makes very inefficient use of the wireless medium. The prior art also causes frequent fluctuations in the transmission data rate, which may lead to buffer overflows and also affect the viewed video quality. The present invention therefore provides an algorithm for selecting a transmission rate for real-time or a/V streaming applications over a wireless link that selects a modulation that maximizes the transmission data rate while reducing packet error rates and reducing data rate fluctuations.

The present invention minimizes packet errors without explicitly measuring the packet error rate. This is done by using a priori (a-priority) information about the performance of the wireless hardware, which works as follows. (examples will be for 802.11x, but may be equally applicable to other wireless technologies).

The transmission to the new remote device may start at the lowest supported modulation/data rate. There are two versions or embodiments of the present invention. In the basic version, the transmitter measures SINR and other data for previous packets, such as ACK packets it previously received from the receiver, and uses these as estimates of the measurements made by the receiver for the packets it receives. A second version of the invention, which is generally more idealized, is for the receiver to measure SINRs etc. and send these back to the transmitter. In a first version of the invention, the transmitter measures the SNR (signal to noise ratio) or RSSI (received signal strength indicator) of the packets it receives from the remote device and ideally also the SINR (signal to interference plus noise ratio) of the signal. Based on the sender's knowledge (or estimation) of the PERs (packet error rates) of the different modulations at different SNR/SINR at the receiver, the sender can estimate the modulation to provide a suitably low PER. The receive sensitivity data describing the SNR at different modulations providing a particular level (e.g., 10%) PER is standard performance data provided by WLAN chipset vendors. The final data for these calculations should take into account the entire system of which the WLAN chipset is a part, e.g. antenna gain.

The above procedure allows selecting a modulation that provides a suitably low PER at a given time instant given the measured SNR/SINR between the wireless transmitter and the wireless receiver. But it does not reduce the modulation fluctuation over time (and thus the fluctuation in data rate and throughput). Movement of objects in the environment (among other reasons) may cause SNR and SINR to vary over time. While such variations should be automatically accounted for by variations in the SNR/SINR determined at the receiver and variations in the modulation of the transmitted data, the transmitter may not be able to sample the RF channel frequently enough so that the SNR/SINR is reduced to a level that causes transmission errors before the channel has been resampled. Sampling of the RF channel occurs during reception of the packet. In the first version of the present invention, each time a TX receives an ACK packet from a receiver, the TX can estimate SINR or the like during reception of the ACK packet; thus, this may occur within 100 microseconds, or may occur after a period of milliseconds or even seconds. In a second version of the invention (described below), the receiver samples the RF channel each time it receives a packet from the TX, and then the receiver sends a summary of its measured SINR etc back to the TX. The sending of the summary information may occur whenever necessary, but in order to not overload the link capacity, it is not usually done so frequently in the order of 1 ms at today's modulation rates.

It is therefore desirable to establish some headroom or safety margin into the estimated modulation. Such headroom factors are also useful for accounting for errors in the data/specification/performance of the wireless chipset and measurement errors due to, for example, varying path delay profiles. This headroom is achieved by subtracting a certain value (e.g., k) from the SNR/SINR measured before finding the appropriate modulation to produce a given PER at that SNR/SINR. The magnitude of k can be considered as a temporal fading margin and can therefore be determined by considering a curve describing the PDF (probability distribution function) of the fading magnitude in the environment and the rate of change of the RF channel in the environment. Thus, k can be determined either by an a priori estimate of the user's RF environment or from actual measurements made during operation of the wireless system in the user's environment.

This additional feature of the present invention (i.e., applying headroom for rate determination) is illustrated in fig. 4 and 5. Fig. 4 is a flow chart of a method of using headroom in the determination of a rate control signal. At step 40, the measured SNR/SINR signal is obtained as described above. The headroom is subtracted from the SNR/SINR value at step 41. The headroom is determined by inputting a priori values (step 42) or from measured data (step 43). At step 44, the resulting SNR/SINR with margin (SNR/SINR-k) is used to determine the rate.

Fig. 5 shows an apparatus corresponding to the method of fig. 4. The SNR/SINR signal (from RX/demod 25) is input to an addition (subtraction) unit 45 of the TX rate control unit 30. The headroom determining unit 46 inputs the headroom value k to the adding (subtracting) unit 45, and the headroom value k is subtracted from the SNR/SINR in the adding (subtracting) unit 45. The headroom determining unit 46 determines the headroom either from an a priori value or from measured data, which are shown as two inputs to the unit 46. The adjusted SNR/SINR value from the adding unit 45 is input to a rate determining unit 47, and in the rate determining unit 47, a rate control signal is generated.

In addition, to prevent too frequent changes to the transmit data rate, the algorithm is modified accordingly. For example, a running average of the past N SINR values may be maintained, and the average may be used to determine the transmission data rate. However, in the case where the current SINR value drops more than M s.d. (standard deviation) units from the moving average, the moving average may be ignored and the actual SINR value used.

This additional feature of the invention (i.e., using the SINR average for rate determination) is illustrated in fig. 6 and 7. Fig. 6 is a flow chart of a method of using SINR averages in the determination of rate control signals. At step 50, the actual (i.e., current) SINR value is obtained. Since the SINR value is obtained, it is stored in step 51 and an average value is obtained in step 52. In step 53, the current actual value is compared with the average value. At step 54, the SINR value to be used for rate determination is selected from the current value and the average value. The average value will generally be selected to reduce fluctuations in the data rate unless a condition for selecting the current value is met, e.g., there is a significant variation from the average value.

Fig. 7 shows an apparatus corresponding to the method of fig. 6. The actual (i.e. current) SINR is input into comparator 56 and also into memory device 57, where the past values are stored in memory device 57. The stored values are averaged in an averaging device 58 and also input to the comparator 56. The comparator output is the SINR value to be used for rate determination. The average value will generally be selected to reduce fluctuations in the data rate unless a condition for selecting the current value is met, e.g., there is a significant variation from the average value. The apparatus of fig. 7 may be placed at the output of SNR/SINR detection block 32 of fig. 3 or at the input of TX rate control block 30 of fig. 3.

Examples of the invention

Current SNR/SINR: -74dBm

Average SNR of past 10 samples: -70dBm

Margin (headroom): 14dBm

Actual "SNR/SINR with margin" to be used: -70-14 ═ 84dBm

Reception sensitivity at 80 dBm: 18Mbps at 5% PER

Ideally, the following is done in a further embodiment of the invention shown in fig. 8 as an improvement to the rate determination based on SNR/SINR/RSSI measurements described above. This is a second version of the invention where the estimate is sent back from RX to TX. At step 60, the remote device sends back to the transmitter the received SNR/SINR of the most recent packet received from the transmitter. Also periodically sent at step 61 is the most recent PER and number of retransmissions since the last such report. Also sent in step 62 is a table comprising PER at different modulations of the specific SINR of the software used at the receiver, i.e. an a priori table of the reception sensitivity of the receiver hardware provided in step 63. The table does not have to be sent with every packet but may be sent only once per session or once during the initial association between the two devices. Ideally, the SNR/SINR information is included in packets that are normally sent to the transmitter, and therefore does not contribute to additional packets. At step 65, the TX rate is adjusted based on all of this information.

As described above, the a priori curve of SNR/SINR versus modulation PER (SNR/SINR vs. modulation vs. PER) from step 63 may be used. The data may also continue to be obtained from the actual data transmission in progress, and the curves may be constructed during the actual transmission, rather than using a priori information, at step 64. Steps 63 or 64 may be used to provide PER to SNR/SINR (PER vs. SNR/SINR) information used in other embodiments of the present invention.

It is also noted that there is an abnormal situation where the quality of the link strength (measured by SNR/SINR) may suddenly drop to a large extent. In this case, the SNR/SINR will not be updated to this new lower value because no new packet being received is detected at all. While in such abnormal situations it is generally not helpful at all to reduce the modulation rate, the present invention does avoid this situation by simultaneously monitoring the packet retransmission rate (provided in step 61). The packet retransmission rates at TX and RX are used to (a) detect when SNR/SINR based methods are inaccurate, in which case alternative actions may be taken (e.g., the margin may be made more conservative), or (b) when the link is completely down.

It should be clear that the logic of the algorithm described herein may be implemented in other variants. In addition, the entire method can be implemented in similar variations.

While the above description contains many specifics, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is therefore to be understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art, and that the scope of the present invention is accordingly limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more". All structural, chemical and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed as conforming to the provisions of the sixth clause of 35 u.s.c.112 unless the element is expressly described by the phrase "means for …".

Claims (20)

1. A method for determining a transmission rate in a wireless communication system, comprising:

initiating transmission at an initial data rate;

transmitting data packets at a selected rate that is initially the initial rate;

receiving the transmitted data packet;

measuring at least one of a signal to noise ratio (SNR) or a Received Signal Strength Indicator (RSSI) or a signal to interference and noise ratio (SINR) to produce a measured SNR/SINR signal; and

adjusting the transmission rate based on the measured SNR/SINR signal and information about Packet Error Rate (PER) as a function of SNR/SINR.

2. The method of claim 1, wherein the data packet is transmitted and received in a wireless communication system executing a real-time streaming application.

3. The method of claim 1, wherein the data packet is transmitted and received in a wireless communication system formed by a Wireless Local Area Network (WLAN).

4. The method of claim 1, wherein the initial data rate is a lowest data rate and the rate is adjusted to a maximum rate that provides a predetermined PER level.

5. The method of claim 1, further comprising determining PER versus SNR/SINR information from the a priori values.

6. The method of claim 1, further comprising determining PER versus SNR/SINR information from measured data from actual transmissions.

7. The method of claim 1, further comprising subtracting a headroom value from the measured SNR/SINR value and using the modified SNR/SINR as a basis for adjusting the transmission rate.

8. The method of claim 7, further comprising determining the headroom either from an a priori value or from measured data.

9. The method of claim 1, further comprising:

calculating an average SNR/SINR value for a plurality of transmitted data packets; and

using the average value as a basis for adjusting the transmission rate.

10. The method of claim 1, further comprising periodically providing a recent number of PER data and data packet retransmissions as a further basis for adjusting said transmission rate.

11. A wireless communication system apparatus, comprising:

a transmitter for transmitting data packets at a selected rate, comprising:

a transmission rate control section that adjusts the transmission rate based on the measured SNR/SINR signal and information on a Packet Error Rate (PER) as a function of the SNR/SINR; and

a receiver for receiving transmitted data packets, comprising:

SNR/SINR detection means for detecting at least one of a signal to noise ratio (SNR) and a signal to interference and noise ratio (SINR) of the received data packet to produce a measured SNR/SINR signal.

12. The apparatus of claim 11, wherein the wireless communication system comprises a real-time streaming system.

13. The apparatus of claim 11, wherein the wireless communication system comprises a Wireless Local Area Network (WLAN).

14. The apparatus of claim 11, wherein the transmission rate control means further comprises an addition element for subtracting a headroom value from the measured SNR/SINR value to produce a modified SNR/SINR, the modified SNR/SINR being used as a basis for adjusting the transmission rate.

15. The apparatus of claim 11, further comprising:

a memory device for storing SNR/SINR values measured for a plurality of transmitted data packets;

averaging means for calculating an average SNR/SINR value for a plurality of transmitted data packets; and

a comparator for comparing a current measured SNR/SINR with the average SNR/SINR and selecting either the current value or the average value as a basis for adjusting the transmission rate.

16. The apparatus of claim 15, wherein the comparator is configured to select the average value unless the current value differs from the average value by more than a preselected value.

17. The apparatus of claim 15, wherein the storage device, averaging device, and comparator are located either at an output of the SNR/SINR detection component of the receiver or at an input of the transmission rate control component of the transmitter.

18. The apparatus of claim 11:

wherein the transmitter further comprises:

a first modulation and transmission section;

a first antenna connected to the first modulation and transmission means;

a first receiving and demodulating part connected to the first antenna;

said transmission rate control means being connected to said first receiving and demodulating means and to said first modulating and transmitting means; and is

Wherein the receiver further comprises:

a second receiving and demodulating section;

a second antenna connected to the second receiving and demodulating part;

a second modulation and transmission section connected to the second antenna;

the SNR/SINR detecting section is connected to the second receiving and demodulating section and to the second modulating and transmitting section;

wherein the measured SNR/SINR signal from the SNR/SINR detecting section is transmitted from the second antenna to the first antenna by the second modulation and transmission section, and is transmitted to the transmission rate controlling section through the first receiving and demodulating section.

19. The apparatus of claim 18:

wherein the receiver further comprises an error detection component connected to the second receiving and demodulating component and to the second modulating and transmitting component; and is

Wherein the transmitter further comprises a retransmission control section connected to the first receiving and demodulating section and to the first modulating and transmitting section;

wherein the error detection section detects an error in the received data packet and generates a retransmission signal, which is transmitted to the retransmission control section, which causes the transmitter to retransmit the erroneous or lost data packet.

20. A wireless communication system apparatus, comprising:

means for transmitting data packets at the selected rate;

means for receiving the transmitted data packet;

means for measuring at least one of a signal to noise ratio (SNR) or a signal to interference and noise ratio (SINR) of the received data packets to produce a measured SNR/SINR signal; and

means for adjusting the transmission rate based on the measured SNR/SINR signal and information on Packet Error Rate (PER) as a function of SNR/SINR.