Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-varying and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. The paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used to perform time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM.

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Broadband MIMO-OFDM wireless communications

we present a medium access control (MAC) protocol for ad hoc networks with multiple input multiple output (MIMO) links. MIMO links provide extremely high spectral efficiencies in multipath channels by simultaneously transmitting multiple independent data streams in the same channel. MAC protocols have been proposed in related work for ad hoc networks with other classes of smart antennas such as switched beam antennas. However, as we substantiate in the paper, the unique characteristics of MIMO links coupled with several key optimization considerations, necessitate an entirely new MAC protocol. We identify several advantages of MIMO links, and discuss key optimization considerations that can help in realizing an effective MAC protocol for such an environment. We present a centralized algorithm called stream-controlled medium access (SCMA) that has the key optimization considerations incorporated in its design. Finally, we present a distributed SCMA protocol that approximates the centralized algorithm and compare its performance against that of baseline protocols that are CSMA/CA variants.

Medium access control in ad hoc networks with MIMO links: optimization considerations and algorithms

A wide band dual-beam microstrip antenna is proposed in this communication. Two radiation beams off broadside are obtained by operating the patch antenna at the higher order TM02 mode instead of the fundamental mode, which radiates a broadside beam. Broadening the antenna bandwidth is achieved by using the U-slot technique. Unlike previous work on the conventional U-slot microstrip antenna, the effect of the U-slot inclusion on the performance of a patch antenna operating at the TM02 mode is studied across the entire achieved bandwidth. The antenna analysis is carried out with the aid of full wave simulation, and an antenna prototype is fabricated and measured for validation. Good agreement between the simulated and measured results is observed. The antenna operating frequency range is 5.18-5.8 GHz with VSWR less than 2, which corresponds to 11.8% impedance bandwidth. It exhibits two radiation beams, directed at 35° and -33° with 7.92 dBi and 5.94 dBi realized gain, respectively at 5.5 GHz.

Wide Band Dual-Beam U-Slot Microstrip Antenna

A novel broadband CPW-fed circularly-polarized slot antenna with an open slot is presented. The broadband circular polarization can be achieved simply by opening the radiation slot at the lower left of slot. From the experimental results, the 3-dB axial-ratio bandwidth can reach as large as 1000 MHz (27% relative to the center frequency of 3700 MHz) which can cover the 3.3-3.8 GHz WiMAX band. In addition, the proposed design has the VSWR ≤ 2 impedance bandwidth of 5330 MHz (111% relative to the center frequency of 4795 MHz) which can cover the 2-6 GHz WiMAX band. The proposed antenna also has a peak antenna gain of about 5.3 dBic and gain variations can be less than 1 dBic for frequencies within the CP bandwidth.

Broadband CPW-Fed Circularly-Polarized Slot Antenna With an Open Slot

A dual-beam filtering patch antenna consisting of a slotted patch, a metal strip underneath the patch, two pins, and a ground plane is proposed for wireless communication application. A wide operation band with stable symmetrical dual-beam far-field radiation pattern is obtained, and two radiation nulls at the lower and the upper band edges, respectively, are controlled to ensure a sharp rolloff rate at the band edges for both reflection coefficient and realize gain. Undesired higher modes can be suppressed over the stopband by changing the spacing between the patch and ground pane With entire height of $0.058~\lambda _{0}$ , the proposed antenna is implemented to show a −10 dB bandwidth of 3.0–3.8 GHz, a consistent realized gain of about 6.8 dBi within the passband for both two radiation beams directed at ±30°, out-of-band radiation suppression level of higher than 17 dBi, and good band-edge selectivity.

Dual-Beam Filtering Patch Antennas for Wireless Communication Application

A multibeam beamformer in combination with a decision feedback equalizer is considered for the base station in a single-cell 100-Mb/s TDMA/TDD QPSK indoor wireless network at 24 GHz. The outage rate in terms of required SNR/bit/antenna is estimated using a statistical, clustered propagation model and for beam selection diversity and two-beam combining.

Multibeam antennas for indoor wireless communications

A multibeam beamformer is considered for the base station in a single-cell 100 Mbps TDMA/QPSK indoor wireless network at 24 GHz. Using a previously reported statistical propagation model that forms clusters of paths in angle and delay, we evaluate the performance of an RF beamformer in combination with a decision feedback equalizer (DFE) for indoor wireless communications. Based on the model, we calculate the required SNR (dB) per bit as a function of the number of beams in the beamformer, amount of tapering on the beams, the number of forward taps in the DFE, and selection combining versus optimal baseband two-beam combining for an outage probability of 10/sup -2/ with a BER threshold of 10/sup -5/.

http://ieeexplore.ieee.org/iel5/6585/17580/00810921.pdf

E.O. Rausch

Papers

Multibeam antennas for indoor wireless communications

Multibeam antenna with decision-feedback equalization for home wireless communications