Seungbeom Lee

Rotating Priority Queue based Scheduling Algorithm for IEEE 802.11n WLAN

The IEEE 802.11 working groups are currently working on the support of quality of service (QoS) and enhancements for higher throughput in a new standard called IEEE 802.11e and IEEE 802.11n, respectively. Although each standard focuses on only the specified issue as mentioned, the wireless LAN (WLAN) products based on IEEE 802.11n have to support both of them. IEEE 802.11n products provide QoS support as well as high throughput with frame aggregation. In this paper, we propose QoS scheduling and frame aggregation algorithm on the basis of rotating priority queue to manage the delay budget and control frame aggregation. Simulation results show the performance improvement of the proposed algorithm in the context of average delay and packet drop rate.

Performance Compensation of IEEE 802.11e QoS stations with Coexistence of Legacy 802.11 stations

This paper shows that the deteriorated performance of IEEE 802.11e QoS stations with coexistence of IEEE 802.11 stations can be compensated by changing the value of AIFS or contention window size of QoS or non-QoS stations in IEEE 802.11e. The performance of IEEE 802.11e QoS stations with coexistence of IEEE 802.11 stations deteriorates compared to the use of only IEEE 802.11e stations. The use of the smaller contention window minimum (CWmin) of QoS, the larger contention window maximum (CWmax) of non-QoS, or the larger AIFS value of non-QoS can compensate the aggregated throughput of QoS stations, respectively.

Adaptive Acknowledgment schemes of the IEEE 802.11e EDCA

The IEEE 802.11e standard adds new optional acknowledgment (ACK) schemes called block ACK and No ACK Although these two schemes offer new data transmission services, there is no description which scheme is the most efficient under the different channel environments. In this paper, we apply the three ACK schemes (including legacy 802.11 ACK scheme) to the contention-based channel; an enhanced distributed channel access (EDCA), in IEEE 802.11e and then analyze the throughput and the packet drop rate, corresponding to the different kind of ACK schemes. Link parameters such as the number of stations, physical layer (PHY) mode, bit error rate (BER) and MAC protocol data unit (MPDU) length are considered. With the numerical results, we determine the adaptive ACK scheme for the different channel environments (represented by BER) in terms of throughput and packet drop rate.

Implementation of the Modified State Mapping Viterbi Decoder with Radix-4

In this paper, the complexity of Viterbi architectures is compared in the point of the survivor sequence management. Moreover, the Viterbi decoder with constraint length (K=7), truncation length (T=5K), and code rate (R=l/3) is implemented. The Viterbi decoder uses the Radix-4 as the ACS method to obtain high throughput and low latency. The modified state mapping algorithm is also applied to achieve low latency as the survivor sequence management.

VLSI Implementation of Area-efficient List Sphere Decoder

Generating soft information in list sphere decoder (LSD) increases the computational complexity to select a specific number of candidate lattice points. Among the techniques to reduce the computational complexity, we find that real-valued operation is able to reduce the per-node complexity, ordering process, and storage elements significantly with some tradeoff in speed degradation compared to complex-valued operation. This is useful in systems using large number of antennas and high-order modulation. This paper presents a real-valued LSD architecture for a mode of 4times4 64QAM and compares the hardware complexity of the proposed architecture to that of complex-valued LSD. Although the processing cycle of the proposed architecture is twice that of complex-valued LSD, the hardware complexity of the proposed architecture is less than a fourth of that of the complex-valued LSD. The proposed architecture is also implemented using 0.25um technology and attains an average throughput of 430 kvectors/sec at a signal-to-noise ratio (SNR) of 20 dB.

Design of Power-efficient Memory-based FFT Processor with New Memory Addressing Scheme

This paper presents a new memory-addressing scheme for the realization of power-efficient memory-based FFT processors. The scheme is based on the minimization of the coefficient access and reduction of switching activity by modifying the butterfly sequence. It also results in reducing hardware scale and shortening the critical path delay. Therefore, the power consumption in complex multiplier and memory is reduced

Effect of Collision on Movement Tracking Using Active RFID Power Measurement

This paper reports preliminary work with an RFID based real time location system (RTLS) designed for location and guidance of people in welfare facilities like the sanatorium which has the both of indoor and out door environment. The system consists of a number of fixed RF readers and a number of active RFID tags carried by the target object, or senior people. We compare the performance of several RTLS schemes which use the received signal strength indication (RSSI) values emitted by the moving active RFID tags. Traditional trilateration, fingerprinting, and well-known LANDMARC approaches are evaluated and compared using the SystemC-based computer simulation. Results show a mean estimated error (MEE) performance of 3m with the 130 tags according to the position updated frequency in our simulation environment.

Software Implementation for Multi-Protocol 13.56 MHz RFID Reader

In this paper, we design and implement a multi-protocol 13.56MHz reader in software. In order to satisfy the timing constraint, three level optimizations called compile level, syntax level, and architectural level optimizations are applied. The execution time of optimized code is reduced by 85%, so that it satisfies timing requirement of a 60MHz speed EISC processor. In addition, the binary code size is minimized to 211KBytes which can be loaded on a 256KB size memory.

Throughput Enhancement of IEEE 802.11 MAC by antenna selection for IEEE 802.11a devices

Recently, IEEE 802.11n system has proposed by demands for high throughput and this IEEE 802.11n system should build upon IEEE 802.11a system. This paper suggested simple way to implement 802.11a backward compatible transmitter diversity using multiple antennas in an 802.11a/802.11n device and simulated how much total throughput is enhanced in 802.11a MAC by using multiple antennas.

Transmission Energy Efficiency in MIMO-OFDM based WLAN with HCCA Channel Access Scheme

Energy consumption is one of the most stringent bottlenecks in wireless communication device. In this paper, we investigate the effect of MAC and Physical layer on power efficiency in MIMO-OFDM based WLAN. Specifically, we study the transmission energy efficiency for several physical mode and power level with the aid of our derived power efficiency model. This analysis addresses the impact of the HCCA MAC protocol with block ACK policy in polled TXOP on the power efficiency of MIMO-OFDM based WLAN