Throughput-Based Antenna Selection Measurements

In this work, we provide a new throughput-based antenna selection criterion that considers the entire system design rather than only the channel state information. The performance evaluation was carried out in a measurement campaign in a common outdoor urban scenario. We present our results in terms of physical layer throughput over transmit power. In addition to diversity gains, we also see gains due to the selection of differently polarized antennas. In terms of SNR, the results show a gain of several decibels depending on the number of antennas selected. I. INTRODUCTION The utilization of Multiple-Input Multiple-Output (MIMO) technologies is continuously growing due to the drastic in- crease in the channel capacity and the enormous improvement in the communication link reliability. Despite these advan- tages, MIMO has been slow in getting adopted in practical wireless systems. Currently, MIMO can be found as an option in High Speed Downlink Packet Access (HSDPA), IEEE 802.16 (WiMAX), future modes of IEEE 802.11 (WiFi), and will be mandatory in next generation cellular systems. One of the main reasons for the slow introduction of MIMO technologies in commercial wireless systems is the required increment in complexity and hardware costs. While antenna elements are cheap and usually small, each one requires a complete radio frequency (RF) chain (low-noise amplifier, frequency down-converter, analog to digital converter, filters, and so on). Unfortunately, RF hardware is expensive compared to the cost of the the digital hardware and does not follow Moore's law (1). Also, introducing new hardware consumes more energy which is very inconvenient for today's hand-held mobile devices. Antenna subset selection (AS) is a promising technique that reduces the MIMO hardware complexity problem. AS adaptively chooses a specific subset of all available antennas, i.e., an Nt × Nr system can be constructed while only Lt × Lr complete RF chains are used at the same time (Lt <N t and Lr <N r). The antenna subset selection is based on a "selection criterion" depending on the application. It has been shown that under most circumstances, AS systems can achieve the same diversity gains as full-complexity systems. On the downside, AS suffers from a loss in array gain (mean SNR gain) but this loss can be avoided by preprocessing in the RF chain (2-6). A. State of the art