Examples

Single-user mode

The graph on the left shows the comparison of system throughputs when one user at a time is scheduled by a base station.

The compared scenarios are: perfect channel state information at the base station, 4 and 2-bit feedback per frame and no channel state information at the transmitter (round-robin scheduling with equal power distribution). The system has been tested with the following parameters:

With only 4 bits feedback, the loss of performance compared to the perfect channel state information is negligible and even reducing it to 2 bits does not introduce significant throughput reduction. When there are many users in the system, throughput with no CSI will not converge to full-CSI throughput for large transmit powers. Even 2 bit feedback brings power gains in the range of up to 5 dB.




Multi-user mode

The graph on the left shows the comparison of system throughputs when two users at a time are scheduled by a base station with the same set of parameters as above. The detection method is a simple thresholding device at each UT. The compared scenarios are: perfect channel state information at the base station, 4-bit feedback per frame with fast changing channel (Doppler offset normalized per frame=0.1), 4-bit feedback with slow changing channel (Doppler offset=0.01) and no channel state information at the transmitter (round-robin scheduling with equal power distribution).

The design of the codebooks for time-correlated channnels (patent pending) allows the system to closely approach theoretical cooperative-system sum-rate with only 4-bits per frame for slower channels. For faster changing channels, the sum-rate can be easily improved by increasing the number of feedback bits per frame.