4G MIMO OFDM - TOPICS IN WIRELESS COMMUNICATIONS A...

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IEEE Communications Magazine • September 2002 143 A Fourth-Generation MIMO-OFDM Broadband Wireless System: Design, Performance, and Field Trial Results 0163-6804/02/$17.00 © 2002 IEEE A BSTRACT Increasing demand for high-performance 4G broadband wireless is enabled by the use of multi- ple antennas at both base station and subscriber ends. Multiple antenna technologies enable high capacities suited for Internet and multimedia ser- vices, and also dramatically increase range and reliability. In this article we describe a multiple- input multiple-output OFDM wireless communi- cation system, lab test results, and recent field test results obtained in San Jose, California. These are the first MIMO system field tests to establish the performance of MIMO communication systems. Increased capacity, coverage, and reliability are clearly evident from the test results presented in this article. I NTRODUCTION This design is motivated by the growing demand for broadband Internet access. The challenge for wireless broadband access lies in providing a com- parable quality of service (QoS) for similar cost as competing wireline technologies. The target fre- quency band for this system is 2–5 GHz due to favorable propagation characteristics and low radio frequency (RF) equipment cost. The broad- band channel is typically non-LOS channel and includes impairments such as time-selective fad- ing and frequency-selective fading. This article describes the physical layer design of a fourth- generation (4G) wireless broadband system that is, motivated from technical requirements of the broadband cellular channel, and from practical requirements of hardware and RF. The key objec- tives of the system are to provide good coverage in a non-line-of-sight (LOS) environment (>90 percent of the users within a cell), reliable trans- mission (>99.9 percent reliability), high peak data rates (>1 Mb/s), and high spectrum efficiency (>4 b/s/Hz/sector). These system requirements can be met by the combination of two powerful technologies in the physical layer design: multi- input and multi-output (MIMO) antennas and orthogonal frequency division multiplexing (OFDM) modulation. Henceforth, the system is referred to as Airburst. Multiple antennas at the transmitter and receiver provide diversity in a fading environ- ment. By employing multiple antennas, multiple spatial channels are created, and it is unlikely all the channels will fade simultaneously. The Air- burst system employs two transmit antennas and three receive antennas at the base station (2 × 3 downlink), and one transmit antenna and three receive antennas at the customer premises equip- ment (CPE) (1 × 3 uplink). Only one transmit antenna is used at the transmitter due to cost considerations. It is seen that spatial diversity in Airburst yields link budget improvements of 10–20 dB compared to a single-input single-out- put (SISO) system by reducing the fade margins.
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4G MIMO OFDM - TOPICS IN WIRELESS COMMUNICATIONS A...

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