Per stream rate control using APP decoding

#1. Field of the Invention

#The present invention generally relates to communication systems and in particular multiple antenna systems.

#2. Description of the Related Art

#FIG. 1 depicts a flow chart of the method of the present invention;

#FIG. 2 shows a probability of codeword error vs. SNR curve for four members of an MCS being used by a communication system applying the method of the present invention.

#The present invention provides a method for efficiently allocating one or more resources to at least one stream of a communication system by performing an APP decoding process at a receiver of the communication system capable of receiving signals from the streams over a communication channel. We describe a process to determine the channel characteristic as seen by each stream thus enabling the proper amount of one or more resources to be allocated to each stream of the communication system. The invention determines the channel characteristic per stream by using Modified Union bounds.

#A modified union bound for each stream is determined where each modified union bound is a function of the following three parameters: (1) the channel matrix as seen by the receiver; (2) the transmit power of the signals from the stream and (3) the variance of the noise in the communication channel assuming that the noise follows Gaussian statistics and has zero mean. A Q(x) function is used to determine the modified union bounds where x represents a combination of the three parameters. Modified union bounds provide an upper bound probability of error (Pe) value of any particular symbol transmitted for a particular stream. Modified union bounds are based on union bounds, which is a well known technique that is used in communication systems determine an upper bound on the probability of error for the collection of symbols transmitted simultaneously in the streams. A transmitted symbol of any particular stream is drawn from a constellation of symbols. A probability of symbol error vs. SNR (Signal to noise ratio) curve is generated for the symbol constellation of a particular stream assuming an Additive White Gaussian Noise (AWGN) channel. SNR is the ratio of the signal power to the noise power. Probability of error versus SNR curves can be obtained by well-known numerical methods and/or statistics. The calculated upper bound probability of error value (Pe) using modified union bounds is applied to the probability of symbol error vs. SNR curve to obtain an SNR value. This SNR value is used to determine a proper data rate for that stream where the data rate is one or more resources that desirably are to be efficiently allocated amongst the streams. The system can choose to transmit the using a set of symbols in accordance with any one of various members of a Modulation and Coding Set (MCS). Each member of the MCS has associated with it a modulation scheme and an error correcting coding scheme. In essence, each member of the MCS defines a particular data rate. Further, each member of the MCS is associated with or can generate a particular set of coded symbols or codewords. A probability of codeword error vs. SNR curve for AWGN channel is generated yielding a set of such curves. The SNR value calculated from the probability of symbol error vs. SNR is applied to the set of curves (probability of codeword error vs. SNR) and the MCS that gives the highest data rate while keeping the probability of error small is chosen for that particular stream. The above process can be repeated for each of the streams allowing the data rate to be calculated for each stream with the APP decoding. Therefore, the appropriate data rate (or other resource) for any stream can be individually determined allowing efficient use of communication system resources.

#For ease of discussion, the method of the present invention will be discussed in the context of a 2×2 antenna system where two transmit antennas are transmitting to two receive antennas over a communication channel having a channel matrix, H. The channel matrix is a well known parameter that characterizes the overall channel between a transmitter and receiver. It should be noted however that the method of the present invention is not limited to antennas or any special type of transmitter device. Further, the method of the present invention is essentially a per stream rate control method in which the origin of a signal stream is not of any consequence and the type of communication system within which the stream is propagating is not of any consequence. Typically, the stream consists of coded symbols that are formed by coding channel bits into symbols by digital modulation and the channel bits are formed from coding information bits by channel coding. In general, the streams are transmitted through multiple transmitters (e.g., antennas) over a communication channel having a channel matrix, H. The method of the present invention is applicable to both flat fading and frequency selective channels.