Abstract-This paper explores channel estimation using superimposed pilots for OFDM systems. The pilots are added linearly to the modulated symbol at a fraction of the total transmit power, making the method spectrally efficient. We present a series of receivers in which complexity is traded for performance; in particular, a receiver that achieves the theoretically lowest BER but has high complexity and a low complexity receiver that shows near optimal performance. We show by simulations that the performance of the receiver is independent of the channel's Doppler frequency and delay spread. We also analytically compute a bound for the bit error rate performance of the proposed receiver.
Abstract-We derive a simple characterization of the diversitymultiplexing (D-MG) tradeoff in three multiuser scenarios -multiple access, broadcast and relay assuming channel knowledge at the transmitters. Specifically, we study the D-MG tradeoff of protocols in literature that opportunistically use the channel knowledge to maximize the information rate. We show that for the multiple access channel with K users, a feedback of log K bits is sufficient to maximize the multiuser diversity gain. The multiuser diversity gains in all three channels are obtained without explicit cooperation between users.
We consider a multiple access channel (MAC) with multiple antennas, where each user has different diversity and multiplexing gain requirement. For this configuration, we characterize the fundamental tradeoff region for each user. Specifically, we compute the maximum achievable diversity gain for a user in a MAC, given an achievable point in the multiplexing gain region.
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