UMTS link-level demonstrations with smart antennas

With the exploration of multiple antennas at transmitter and possibly also at receiver end, the original concept of UMTS (universal mobile telecommunications system), specified within 3GPP (3rd-generation partnership project), needs to be reconsidered. While the so-called MIMO (multiple-input multiple-output) techniques promise huge improvements in spectral efficiency, in general, once constraints by standards are specified, it can become quite cumbersome to achieve such improvements. The success of MIMO techniques in UMTS depends on the availability of technically feasible and affordable solutions. The terminal side needs special attention due to its limitations in computational and battery power. In general, MIMO algorithms are rather complex, making their implementation as FPGA or ASIC difficult. Therefore, low-complexity solutions for MIMO systems attract more and more attention. In this chapter, steps towards integrated circuit solutions for MIMO systems are reported. The discussion starts with a review of a state-of-the-art UMTS SISO (single-input single-output) mobile terminal in Section 37.1. RF (radio frequency) as well as baseband signal processing challenges and requirements are addressed. Furthermore, principle RFIC (radio frequency integrated circuit) and baseband chip architectures, with particular regard to the RAKE receiver, are discussed. In Section 37.2 the SISO RAKE concept is extended to the SIMO (single-input multiple-output) case, which is especially of interest for the uplink. Space-time (ST) RAKE receivers for UMTS base stations (node B) are presented. General MIMO system considerations covering RF aspects as well as baseband MIMO decoding techniques, including their implementation constraints, are highlighted in Section 37.3. In addition, insight in the complexity of MIMO decoding algorithms is provided. First realizations of UMTS MIMO prototypes and even ASICs are reported on in Section 37.4.