An Application Specific Instruction Set Processor Based Implementation for Signal Detection in Multiple Antenna Systems
In comparison to single antenna systems, a wireless multiple-input multiple-output (MIMO) system provides higher throughput at no additional cost of bandwidth, but the high complexity of the detection algorithms poses a major challenge to the hardware implementation. Maximum likelihood (ML) MIMO detection guarantees optimal performance but implies huge processing complexity, which makes acceptable this approach only when the number of transmitting antennas is low and the adopted modulation scheme has a small cardinality. Sphere decoding (SD) is an efficient method that significantly reduces the average processing complexity with no performance penalty. Most of known sphere decoders have been implemented as application specific integrated circuits (ASICs), but the need for high degree of flexibility in MIMO detection makes interesting also application specific instruction set processor (ASIP) implementations. A single programmable ASIP can hardly reach the same processing speed as a fully dedicated ASIC; thus, parallel architectures with multiple concurrent ASIPs must be conceived to guarantee sufficient data throughput. The objective of this paper is to present a new ASIP-based implementation for the detection of MIMO signals. The processor supports multiple lattice modulation schemes (up to 64-QAM) and up to 4 transmitting antennas and it is able to run both ML and close to ML algorithms. A parallel architecture has been also designed with multiple ASIPs, which concurrently execute the detection algorithm on received symbols, a central unit acting as task scheduler, and a buffer for the compensation of non constant throughput. A dedicated bus handles the communication among allocated units. Each ASIP occupies a silicon area of 0.093 mm2 and runs at 400 MHz when implemented on a 90 nm CMOS technology. Achievable throughput depends on the adopted MIMO system and on the number of allocated ASIPs: a detector with 10 ASIPs programmed to run ML detection on a 4 ×4 MIMO system with 64-QAM modulation offers a throughput of 78 Mbps at signal–to–noise ratio SNR=18 dB.