Tsung-Yu Tsai

Introduction to Packet Scheduling Algorithms for Communication Networks

As implied by the word “packet scheduling”, the shared transmission resource should be intentionally assigned to some users at a given time. The process of assigning users’ packets to appropriate shared resource to achieve some performance guarantee is so-called packet scheduling. It is anticipated that packetized transmissions over links via proper packet scheduling algorithms will possibly make higher resource utilization through statistical multiplexing of packets compared to conventional circuit-based communications. A packet-switched and integrated service environment is therefore prevalent in most practical systems nowadays. However, it will possibly lead to crucial problems when multiple packets associated to different kinds of Quality of Service (QoS) (e.g. required throughput, tolerated delay, jitter, etc) or packet lengths competing for the finite common transmission resource. That is, when the traffic load is relatively heavy, the first-come-first-serve discipline may no longer be an efficient way to utilize the available transmission resource to satisfy the QoS requirements of each user. In such case, appropriate packet-level scheduling algorithms, which are designed to schedule the order of packet transmission under the consideration of different QoS requirements of individual users or other criteria, such as fairness, can alter the service performance and increase the system capacity . As a result, packet scheduling algorithms have been one of the most crucial functions in many practical wired and wireless communication network systems. In this chapter, we will focus on such topic direction for complete investigation. Till now, many packet scheduling algorithms for wired and wireless communication network systems have been successfully presented. Generally speaking, in the most parts of researches, the main goal of packet scheduling algorithms is to maximize the system capacity while satisfying the QoS of users and achieving certain level of fairness. To be more specific, most of packet scheduling algorithm proposed are intended to achieve the following desired properties: 1. Efficiency: The basic function of packet scheduling algorithms is scheduling the transmission order of packets queued in the system based on the available shared resource in a way that satisfies the set of QoS requirements of each user. A packet scheduling algorithm is generally said to

Proximity-Based Service beyond 4G Network: Peer-Aware Discovery and Communication Using E-UTRAN and WLAN

The arising proximity-based applications and services represent a recent and enormous socio-technological trend that has been generating innovative business models for the mobile networks. This paper proposes a WLAN-based beyond 4G (B4G) network architecture for proximity-based service (ProSe) where WLAN serves as the direct communication radio access technology between user equipment. The peer-aware discovery and communication are supported by an integrated long-term evolution (LTE) evolved packet system (EPS) and WLAN. Regarding the realization of ProSe in B4G network, the main advantages of the proposed solutions are twofold: 1) faster time-to-market and 2) utilizing unlicensed spectrums for proximity-based services in B4G network.

Design of a Packet Scheduling Scheme for Downlink Channel in IEEE 802.16 BWA Systems

A packet scheduling scheme in the downlink channel for IEEE 802.16 is proposed.The scheme can be implemented in the base station and is compatible to the MAC protocol of IEEE 802.16. In order incorporate the properties of location-dependent and burst error of wireless channels, we design a novel packet scheduling algorithm named the credit-based algorithm (CBA) to guarantee QoS of both real-time and non-real-time services. Simulation experiments are conducted to evaluate the performance of the proposed scheme. Based on the simulation results, we show the CBA scheme is capable of providing significantly improved system capacity,guaranteeing the packet delay for real-time services, and maintaining fair capacity allocation to non-real-time services.

Condensed Downlink MAP Structures for IEEE 802.16e Wireless Metropolitan Area Networks (MANs)

The new mobile wireless metropolitan area network (WMAN) architecture imposes a demanding performance requirement on the radio resource to provide broadband internet access. The radio resource is partitioned as bursts in time and frequency domains and used by mobile stations (MS) in an exclusive manner. The base station (BS) functionally serves as a resource controller for traffic to and from the MSs associated with it, and thus naturally generates the proper downlink (DL) and uplink (UL) MAPs for active MSs based on service and traffic requirements. However, the DL-MAP construction scheme in IEEE 802.16e OFDMA standard, which was designed for handling irregular traffic pattern of MS, often produces a large DL-MAP, as a certain small amount of data distribution to MSs will render a potential overhead of information elements (IE) in DL-MAP and limit the overall capacity. Moreover, the robustness requirement on MAP broadcasting would further cause severe system overhead. As a solution, we propose two exclusive condensed DL-MAP structures, which only carry partial information of each rectangular burst in order to reduce the size of IE in DL-MAP. For each condensed DL-MAP structure, the algorithms for BS to produce the condensed DL-MAP structure and the scheme for MS to precisely reconstruct the original DL-MAP structure are provided. As confirmed by the analytical results, the proposed condensed DL-MAP can achieve significant DL-MAP size reduction compared with standard DL-MAP structure.

Design and analysis of low-complexity blind beam steering scheme for receive beamform

The complexity of beamforming, such as complexity complex weighting and combining process, are extremely important for implementation. This work presents a low complexity time-domain statistic noise suppression and hierarchical beam search algorithm to improve performance in receivers. For SIMO-OFDM systems, the complexity of the hierarchical beam search algorithm is O(n2log2n). This work proposes a simple hierarchical beam search to find the best steering vector. Through performance evaluation, the BER performance is significantly improved with about 3dB under 10^-5 BER in the case that L1=6 and L2=2 compared to that in the case L1=4 and L2=2. Besides, the BER performance is already quietly close to that achieved by the ideal beamform in the case of L1=6 and L2=4. This setting is a good choice which achieves a good tradeoff between the performance and the computational complexity. In addition, this algorithm is well-matched to different specifications.

A Novel Description approach based on sorted rectangles for scheduling information bearing in OFDMA systems

Dynamic time/frequency resource allocation has been widely employed in wireless OFDMA systems. In such mechanisms, sophisticated scheduling decisions need to be conveyed to users and may lead to considerable signaling overhead. In this paper, a new efficient approach, namely, Sorted-Rectangle Description (SRD) is proposed for describing the scheduling decision in an OFDMA frame. SRD first partitions a frame into minimum number of rectangular polygons, namely, rectangular bursts (RB), in which each RB contains the resource units belonging to the same assignment. We show that each RB-partitioned frame is sufficient to be fully reconstructed by the top-left coordinates of each RB in a specific sorted order. Sorting and reconstructing algorithms with linear time complexity in the total number of RBs are also proposed. Simulations based on a multi-user OFDMA system with full-buffer or periodic small-data traffic model are conducted to evaluate the performance of the proposed SRD method under two representative scenarios. The simulation results show that, for the full-buffer traffic model with a proportional fair (PF) scheduler, the proposed description approach can achieve significant reduction of the overhead ratio compared to that of the existing systems and is expected to lead to considerable increase of system throughput. Meanwhile, for the periodic small-data traffic model, it is shown that the proposed description approach can greatly reduce the rate of packet loss due to timeout or buffer overflow and thus provides significant improvement of the system capacity.

A Probe-and-Update Method for Tuning Analog Self-Interference Canceler in Full-Duplex Radio Systems

Accurate self-interference (SI) cancellation is one of the main challenges for the implementation of full-duplex radio (FDR) systems. In this letter, we proposed a new algorithm, called, probe-and-update method (PUM), to tune the gains of a multi-tap analog SI cancellation filter for orthogonal frequency division multiplexing FDR systems. PUM performs a novel gain updating procedure based on the comparison of two consecutive measurements of the residual SI power, namely, the probe value. Via sufficient number of updates, PUM could approach the minimum average residual SI power. PUM is applicable in a multipath environment and no channel knowledge is needed in advance, which considerably facilitate the implementation. Simulation results show that PUM could achieve a reasonably low residual SI power down to 5.5 dB of the noise floor in a 20-MHz system.

A blind statistical approach for optimal receive beam steering in multipath environments

A novel blind statistical algorithm for obtaining the optimal receive beam vector with maximum time-domain effective SNR in OFDMA systems under multipath environment is proposed. The basic procedure of the proposed approach is obtained via the coarse cyclic prefix (CP) detection first and the sample average of the correlation matrices is calculated from selected signal samples for later singular value decomposition (SVD) on the averaged correlation matrix. The proposed approach has the following advantages: First, it is accurate even in the presence of high noise power and when the process of the OFDMA sampled signals are not white (i.e. not all subcarriers are allocated for data transmission). Secondly, it can be operated in time-domain with no training signals and no pre-assumption of the antenna array structure. Hence, it could be applied directly to a variety of existing OFDMA systems and its design can be made relatively simple for implementation. Theoretical proofs of its optimality and the guarantee of convergence are also provided in this paper. Finally, simulation results verifies the theoretical analysis and shows that the proposed approach can accurately achieve a near optimal SNR gain even in low SNR environment and has a convergence speed within two OFDM symbols.

Low-complexity beam steering algorithm based on binary search strategy for receive beamform

The complexity of beamforming, such as complexity complex weighting and combining process, are extremely important for implementation. This work presents a low complexity time-domain statistic noise suppression and beam steering algorithm based on binary search strategy to estimate the optimal beam vector at the receivers. The beam steering algorithm based on binary search strategy could achieve closely (about 99%) optimal SNR gain within only two binary search. It is desirable choice to archive the suitable trade-off between the performance and the processing overhead. Hence, it could obtain a near-optimal performance with considerably low complexity and high convergence speed. In addition, this algorithm is well-matched to different specifications.

Preamble reconstruction method for impulsive interference avoidance in MIMO-OFDM receivers

For wireless packet transmissions, preambles are essential to make packet synchronization function. Impulsive interference not only distorts datum, but also degrades link reliability. To deal with such distortions, a peak-to-average ratio (PAPR) detection is adopted to search impulsive positions and the convolution with the estimated time-domain response is used to recovery the distorted preambles. Simulations of a 2×2 MIMO-OFDM system with RF impairments in frequency-selective fading indicate that the SNR loss is about 2.5 dB ~ 4.6 dB to ensure synchronization working at a signal-to-impulse ratio (SIR) of -10 dB.