QUANTIZED CHANNEL STATE INFORMATION PREDICTION IN MULTIPLE ANTENNA SYSTEMS
A CSI vector quantizer (VQ) system is provided for time-correlated channels. The VQ system operates a receiver forwarding quantized channel state information in the form of indices and a transmitter predicting channel state change. The VQ system is aimed at feedback channels, in which bit errors, erasures and delays can occur. The VQ system uses transmitter-side channel prediction algorithms that work with the quantized CSI information and allow the system to recover from feedback channel transmission errors, erasures and delays. Moreover, the techniques can be used to lower the required feedback rate, while keeping the system's throughput at the required level.
1 . A method of producing a set of information to be used for predicting feedback concerning channel state information in a multiple antenna communication system, the method comprising:
obtaining feedback concerning channel states;
measuring a frequency of patterns of the feedback; and
recording information concerning the frequency of the patterns of the feedback, wherein the patterns are sequences of adjacent indices followed by a final index.
2 . The method of claim 1 wherein said feedback concerning channel states comprises at least one of an actual set of feedback or a simulated set of feedback.
3 . The method of claim 1 wherein the recorded information concerning the frequency of the patterns of feedback comprises at least a record of the most frequent final index following each of several sequences of adjacent indices, and the record is stored in a matrix.
4 . The method of claim 1 wherein the recorded information concerning the frequency of the patterns of feedback comprises at least a record of the frequencies of one or more final indices following each of several sequences of adjacent indices, and the record is stored in a matrix.
5 . The method of claim 1 wherein the recorded information concerning the frequency of the patterns of feedback comprises at least a record of a list of final indices following each of several sequences of adjacent indices, and the record is
stored as a dictionary of phrases, each phrase comprising a record of a sequence of several adjacent indices followed by a final index.
6 . The method of claim 5 wherein the phrases vary in length according to the length of the sequence that is required in order for the final index following the sequence to be unique in the actual or simulated set of feedback.
7 . The method of claim 1 , further comprising updating the set of information during the operation of the multiple antenna communication system, further comprising the steps of:
receiving feedback concerning channel states; and
updating the recorded information concerning the frequency of the patterns of feedback according to the feedback received.
8 . The method of claim 7 wherein as new feedback is received, information concerning the frequency of patterns from older feedback, or from the actual or simulated set of feedback originally used to produce the set of information, is discarded.
9 . A method of predicting channel state information in a multiple antenna communication system, comprising:
producing a set of information to be used for predicting feedback concerning channel state information in the multiple antenna communication system by obtaining feedback concerning channel states, measuring a frequency of patterns of the feedback, and recording information concerning the frequency of the patterns of the feedback;
receiving sequences of indices; and
using the set of information, predicting a further index.
10 . The method of claim 9 wherein codeword indices received from individual users are predicted.
11 . The method of claim 9 wherein indices of modulation matrices chosen by a transmitter are predicted.
12 . The method of claim 9 , further comprising recovering from a feedback error in the multiple antenna communication system, wherein a received index representing information concerning a channel state has been determined to be erroneous, including:
making one or more attempts to predict an index appropriate for the channel state; and
choosing an index representing a channel state according to the one or more attempts as follows:
in the case that an attempt to predict fails, choosing an index that has previously been used,
in the case that there is a single predicted index, choosing the single predicted index, or
in the case that there are more than one predicted indices, choosing a maximum number of bit errors to consider, and choosing a predicted index from the more than one predicted indices that could have resulted in the received index with a number of bit errors less than the maximum number of bit errors to consider, and if there is no predicted index that could have resulted in the received index with a number of bit errors less than the maximum number of bit errors to consider, choosing any one of the more than one predicted indices.
13 . The method of claim 9 , further comprising compensating for feedback error in a multiple input transmission system, including:
receiving feedback concerning a channel state;
determining whether a feedback error occurred using one or more of the methods of:
using an error detecting code; or
predicting the channel state and determining whether the feedback agrees with the prediction; and
if a feedback error was detected, determining what the feedback would have been without the error.
14 . The method of claim 13 wherein the channel state is predicted by receiving sequences of indices and, using a record of frequencies of patterns of actual or simulated feedback, predicting a further index.
15 . The method of claim 13 wherein the channel state is predicted by:
making one or more attempts to predict an index appropriate for the channel state; and
choosing an index representing a channel state according to the one or more attempts as follows:
in the case that an attempt to predict fails, choosing an index that has previously been used,
in the case that there is a single predicted index, choosing the single predicted index, or
in the case that there are more than one predicted indices, choosing a maximum number of bit errors to consider, and choosing a predicted index from the more than one predicted indices that could have resulted in the received index with a number of bit errors less than the maximum number of bit errors to consider, and if there is no predicted index that could have resulted in the received index with a number of bit errors less than the maximum number of bit errors to consider, choosing any one of the more than one predicted indices.
16 . A method of producing a set of information to be used for predicting feedback concerning channel state information in a multiple antenna communication system, the method comprising:
receiving a channel code index;
obtaining feedback concerning channel states based on the received channel code index;
measuring a frequency of patterns of the feedback; and
recording information concerning the frequency of the patterns of the feedback, wherein the patterns are sequences of adjacent indices followed by a final index.