Standardization of MIMO-OFDM Technology

Abstract

Standards development organizations around the world are making rapid advances in adopting MIMO-OFDM as the technology of choice for emerging broadband wireless standards. These include IEEE 802.11n - the next generation standard for wireless local networking, IEEE 802.16e - a new standard for metropolitan area networks, and 3 GPP Long Term Evolution (LTE) - the next generation standard for cellular networking. When multiple antennas are deployed at the transmitter, they can be used to increase data rates and/or enhance link robustness. Data rates can be increased by using space division multiplexing, which requires standardization. Link robustness can also be enhanced through transmit beamforming, which requires channel state information at the transmitter. FDD systems generally require standardization, but TDD systems also benefit from standardization. Transmit diversity techniques also enhance link robustness. However, some transmit diversity techniques require standardization (such as space time block coding), whereas some do not (such as delay diversity). In this tutorial, we will discuss the various flavors of MIMO-OFDM that are being standardized in 802.11n, 802.16e, and LTE. We will describe in detail the similarities and differences of these systems. For example, 802.11n is a TDD based system and only supports one user in the channel at any given time. LTE, on the other hand, is primarily an FDD based system, and aims to support multiple users in the channel at any given time. Hence, the concept of centralized control with multi-user MIMO is being developed within LTE and 802.16e, whereas 802.11n with decentralized control only supports single-user MIMO. However, space division multiplexing is similar across 802.11n, 802.16e, and LTE.