Jung-Bo Son

Fast automatic gain control employing two compensation loop for high throughput MIMO-OFDM receivers

The performance of a receiver front-end limits the quality and range of the given communication link. An appropriate design based on well-defined system parameters and architecture can make a huge difference in the performance, cost and marketability of the entire system. In particular, there is a need for improved digital automatic gain control (AGC) for use in multi input multi output orthogonal frequency division multiplexing (MIMO-OFDM) systems with application to wireless local area networks (WLANs), targeted for the upcoming 802.11n standard based in H. Yu et al. (2004) and H. Yu et al. (2005). In this paper, we propose an efficient algorithm and implementation of the digital AGC for next generation WLANs. The proposed AGC algorithm has two feedback loops for gain control to improve convergence speed, and at the same time maintains the stability of the AGC circuit. Also, a complete set of parameters for practical implementation is obtained by various experiments with fixed point constraints and accuracy requirements

An Effective Polling Scheme for IEEE 802.11e

In medium access control (MAC) protocols for wireless local area networks (WLANs), the Round-Robin scheme is the general polling scheme. A major drawback of this scheme is that it is inefficient when only a small number of stations have packets to transmit. This inefficiency is caused by polling stations that have no packets to transmit. This paper proposes an effective and simple polling scheme to reduce the number of polling times for a station with no packets to transmit. For example, the simulation result shows that the throughput increases by 35.8% when fifteen stations out of thirty stations in the polling list have packets to transmit at IEEE 802.1 la 54 Mbps rate.

A Novel ZF Detection Scheme for Double SFBC based OFDM System in Frequency Selective Fading Channel

In this paper, we propose an efficient low complexity MIMO detection method for double space-frequency block coded (D-SFBC) OFDM system. The proposed MIMO detector involves three-step filtering process to efficiently de-correlate spatially-multiplexed / space-frequency-coded signals without direct matrix inversion process. As the proposed MIMO detector takes advantage of frequency selectivity, not a favorable channel condition for SFBC system, performance degradation caused by low correlation between two consecutive subcarriers is compensated by assigning weighting factor for every subcarriers in frequency domain. From computer simulation results, our scheme in D-SFTD outperforms previously proposed suboptimal MIMO detection methods such as iterative interference cancellation based V-BLAST.

Analysis of Power Consumption and Efficient Power Saving Techniques for MIMO-OFDM-Based Wireless LAN Receivers

In this paper, we express the power consumption for the wireless receiver employing multiple antenna technique as a closed form function of the number of antennas, time duration, power dissipation for carrier sensing and data decoding, and the probability of successful carrier sensing. Based on the analytical model, we show that when MAC level power save mode is combined with PHY level power save mode utilizing the correlation based carrier sensing indicator, the proposed cross layer power saving technique improves the power efficiency of the wireless receiver. In this paper, we show that the proposed cross layer method improves power at about 15% and 7% efficiency compared to MAC level and PHY level power save mode, respectively.

Efficient block size based polling scheme for IEEE 802.11e wireless LANs

In the recent draft of the 802.11e MAC (2004), the hybrid coordinator (HC) gives transmission opportunity (TXOP) for a station to transmit burst frames for improving throughput efficiency. To use this block ack mechanism efficiently, the relationship of throughput and relative parameters is analyzed, and the throughput efficient condition is evaluated [Il-Gu Lee et al., 2004]. In this paper, we proposed an efficient block size based polling scheme using an adaptive algorithm to improve the aggregate throughput and to reduce the polling overheads without degrading throughput and delay.

ASIC Implementation and Verification of MIMO-OFDM Transceiver for Wireless LAN

In this paper, we describe the implementation and validation of the next generation wireless local area network (WLAN) physical (PHY) layer transceiver using a dual-band and multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) scheme. The maximum data rate of the designed system is 270 Mbps in 40 MHz bandwidth and 2 streams mode. It uses 2 transmit and 3 receive antennas due to reasonable complexity and performance. For implementation and verification of this system, we set up the design flow. To reduce the design time, we propose intermediate design steps which use conventional C language by devising a few rules for hardware description. The system performance is measured from the generated C simulator. We implement all circuits in a single chip.

Design and Verification of High Throughput Transceiver for Next Generation Wireless LAN

In this paper, we describe the design and verification of the next generation wireless local area network (WLAN) physical (PHY) layer transceiver using a dual-band and multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) scheme. The maximum data rate of the designed system is 243 Mbps in 40 MHz bandwidth and 2 streams mode. It uses 2 transmit and 3 receive antennas due to reasonable complexity and performance. For implementation and verification of this system, we set up the design flow. To reduce the design time, we propose intermediate design steps which use conventional C language by devising a few rules for hardware description. The system performance is measured from the generated C simulator. We implement all circuits in Xilinx FPGAs.

Field Test and Experimental Characterization of 5GHz RF Transceivers for Coverage Extension

The characterization for the coverage and performance of RF transceiver is an important step in wireless network design. We present that the enhanced receiver sensitivity utilizing an external LNA and improved transmit power can extend the coverage to meet the achievable performance in the real radio environment.

An Low Complexity Hardware Implementation of MIMO Detector with Application to WLAN

In this paper, we describe a FPGA implementation of MIMO detector for future wireless communication system with application to wireless LAN, targeted for upcoming 802.11n standard. The MIMO detector assumes 2 transmit and 3 receive antennas. In soft-output demapper, we apply channel state information which effectively weights reliability information to soft-decision output bits for enhanced link-level performance. The implementation complexity is significantly reduced by avoiding repeated pseudo-inverse calculation for interference cancellation of every received symbol vector. Furthermore, the overall processing time and fabrication area it takes can be significantly reduced by applying bit reduction technique

Design and Implementation of Robust Time/Frequency Offset Tracking Algorithm for MIMO-OFDM Receivers

In this paper, the robust time and frequency offset tracking algorithms and architecture for high throughput wireless local area network (WLAN) systems are presented. The designed architecture has feedback and feed forward compensation loop with well defined loop filter coefficients obtained by various experiments for practical implementation. Considered functional blocks include residual CFO estimator, carrier phase estimator, and timing error estimator. In addition to the algorithm descriptions of these blocks, the implementation method is presented, as they are modeled in the floating/cycle and bit true fixed point C model. These C models have been used as a reference for RTL coding and its verification. The design has been implemented successfully on an FPGA device. The proposed tracking method produces results very close to that of the offset-free system