Configurable Transmitter and Systolic Channel Estimator Architectures for Data-Dependent Superimposed Training Communications Systems

In this paper, a configurable superimposed training (ST)/data-dependent ST (DDST) transmitter and architecture based on array processors (APs) for DDST channel estimation are presented. Both architectures, designed under full-hardware paradigm, were described using Verilog HDL, targeted in Xilinx Virtex-5 and they were compared with existent approaches. The synthesis results showed a FPGA slice consumption of 1% for the transmitter and 3% for the estimator with 160 and 115？MHz operating frequencies, respectively. The signal-to-quantization-noise ratio (SQNR) performance of the transmitter is about 82？dB to support 4/16/64-QAM modulation. A Monte Carlo simulation demonstrates that the mean square error (MSE) of the channel estimator implemented in hardware is practically the same as the one obtained with the floating-point golden model. The high performance and reduced hardware of the proposed architectures lead to the conclusion that the DDST concept can be applied in current communications standards. 1. Introduction Presently, there is need to develop communications systems capable of transmitting/receiving various types of information (data, voice, video, etc.) at high speed. Nevertheless, designing these systems is always an extremely difficult task, and, therefore, the system must be broken down into several stages each with a specific task. The complexity of each stage is higher when the system operates in a wireless environment because the additional challenges that should be facing due to the complex nature of the channel and its susceptibility to several types of interference. As it is not possible to avoid the influence of the channel on a transmitted data sent through it, an option is to characterize the channel parameters with enough precision so that their effects can be reverted in the receiver. For that reason, channel estimation stage is a key part of any reliable wireless system because a correct channel estimation leads to a reduction of the bit error rate (BER). The channel estimator must deal with multiple phenomenas, such as multipath propagation and frequency Doppler (due to the mobility of the users). In order to deal with these problems, current communication standards specify the transmission of pilot signals which are known in the receiver, allowing an ease estimation of the communication channel. The way of transmitting such pilot signals can be classified in to two major branches: pilot-assisted transmission (PAT)—where pilot and data signals are multiplexed in time, frequency, code, space, or in a combination of the mentioned