David Shiung

A dynamic resource reservation scheme with mobility prediction for wireless multimedia networks

To reduce the call blocking probability (CBP) and call dropping probability (CDP) of real-time and non-real-time traffic in wireless multimedia networks, resource reservation is frequently employed to achieve both the above-mentioned goal as well as to avoid long latency of path rebuilding. However, pure resource reservation may lead to inefficient resource utilization and increase of CBP and CDP due to frequent handoff in wireless networks. To reduce unnecessary resource reservation, the prediction of moving direction can be incorporated to enhance the pure resource reservation. Therefore, a dynamic resource reservation scheme with mobility prediction is proposed in this paper. In this scheme, a resource request with available range rather than a fixed resource request is specified by each traffic to make the reservation scheme flexible. Using simulation results, we show that mobility prediction can dynamically adjust resource reservation and effectively enhance system resource utilization. Moreover, the available interval of resource request gives flexibility to resource reservation which also improves the system performance.

A Dynamic Resource Reservation Scheme Designed for Improving Multicast Protocols in HMIPv6-Based Networks

This paper aims at proposing a dynamic resource reservation scheme to enhance wireless multicasting protocols run in the hierarchical mobile IP version 6 (HMIPv6) based networks. The novelty of this scheme relies on techniques of dynamic resource reservation, priority, pre-registration, and path prediction, which are used to improve wireless multicasting and guarantee service continuity. Through numerical examples, we demonstrate that the proposed scheme performs well in terms of robustness, adaptiveness, and quality of service (QoS) guarantee

Interference Reduction for Terrestrial Cellular CDMA Systems via High Altitude Platform Station

In a cellular code division multiple access (CDMA) system, uplink capacity is limited by interference. For a ground-based CDMA system or a high altitude platform station (HAPS) CDMA system, the interference is contributed by users in the same cell and in other cells. In this paper, a novel scheme is proposed to reduce both the same-cell and other-cell interferences in a cellular CDMA system. The proposed scheme attempts to lower the required transmitting power for each user by integrating terrestrial base stations (BSs) with a HAPS to provide two separate paths for signal reception. Numerical results show that the total interference is significantly reduced and the uplink capacity is improved under the proposed scheme, compared to either a HAPS CDMA system or a ground-based CDMA system.

Filtering tricks for FSK demodulation

In this article, we present a useful trick to make the implementation of a digital noncoherent frequency shift keying (FSK) demodulator more economical from a hardware complexity standpoint, with the goal of minimizing its computational workload. The article also utilizes comb filters in removing the dc offset from the signals and in reducing the complexity of follow-on filtering. The corrected signal is amenable to additional processing at the IF frequency or may be down-converted to a baseband frequency for further processing.

Cascading Tricks for Designing Composite Filters with Sharp Transition Bands [sp Tips&Tricks]

This article presents novel tricks regarding cascading two digital filters to produce composite filters with very sharp transition bands for high-performance applications. The key point of the proposed tricks is to shape the magnitude frequency response of a prototype infinite impulse response (IIR) filter by a two-tap finite impulse response (FIR) filter using its nulls. In particular, we choose either a comb filter or a complementary comb filter of coefficients +1/-1, also called a shaping filter, to sharpen the transition bands of a prototype filter. The magnitude frequency response of the shaping filter compensates the Gibbs phenomenon commonly appearing in the passband edge and produces sharp transition bands for the cascaded filter. As compared to an equivalent IIR filter, the price paid is an additional comb/complementary comb filter of low complexity.

Transmit Power Allocation for Cognitive Radios Under Rate Protection Constraints: A Signal Coverage Approach

Enhancing the transmission rate for a better spectral utilization is always the ultimate goal of any wireless network. In this paper, we consider the problem of optimal power and rate allocation to maximize the transmission rate of a cognitive radio (CR) operating in the spectrum sharing (SS) CR network (CRN). Unlike previous literature that takes into account the amount of interference to the primary system (PS) as the protection criterion, we reconsider the protection to the PS and CRs through different levels of protection in signal-to-interference-plus-noise ratio (SINR). We propose the concept of effective signal coverage called the permissible space for optimal power and rate adaption. The permissible space for a cognitive transmitter spans over a 3-D space, and it varies according to the channel statistics. Through detecting to which permissible space the cognitive receiver belongs, a novel algorithm suited for distributed CR operation is proposed. Numerical results confirm that our algorithm implemented in the SS CRN achieves a significant enhancement in sum rate, as compared with that of an opportunistic spectrum access (OSA) CRN.

Joint Power and Rate Adaptation in a Cognitive Radio Network: The Rate-Distance Approach

In this paper, we study the joint power and rate adaptation in a cognitive radio network (CRN) using the rate-distance nature as the central criterion. The rate-distance nature describes the relationship between transmission rate and signal strength and can further enhance the spectrum efficiency. A general channel model considering composite effects such as distance-dependent pathloss, large-scale shadowing, and small-scale fading is considered. Through emitting a pseudo-carrier, the cognitive radio (CR) transmit-receive (T-R) pair determines the maximal allowable transmission power and thus transmission rate for maximizing the sum-rate of the CRN with guaranteed bit error rate (BER) and outage probability of signal-to-interference ratio (SIR). The proposed algorithm is suitable for real-time adaptation and a maximal sum-rate of the CRN is achieved.

A four-way-polling QoS scheduler for IEEE 802.11e HCCA

In IEEE 802.11e, a centralized polling based channel access mechanism is provided for the quality-of-service (QoS) provision of real-time applications. In order to improve bandwidth efficiency of polling for uplink variable bit rate (VBR) sources, it has previously been proposed in, e.g., ARROW, that the amount of backlogged traffic is fed back for exact bandwidth allocation. However, due to that the feedback and the bandwidth allocation are performed separately in two different polls, transmission latency incurred by packets could cause them to violate delay constraint. In this paper, a four-way-polling scheduler is first proposed by directly inquiring buffer occupancy information of an uplink station during a poll. Theoretical analysis is then performed to evaluate the performance of both the proposed scheduler and ARROW. From both analytical and ns-2 simulation results, it is shown that packet loss rates can effectively be reduced and more capacity can thereby be obtained under the proposed scheduler, as compared with ARROW.

On the optimal power allocation of a cognitive radio network

It is well known that a cognitive radio network (CRN) may further enhance the sum spectral efficiency using temporarily idle spectrum. However, we usually ignore the spatial domain behaviors to fully utilize the radio resource to approach available system capacity. When a signal is transmitted, we usually treat its occupancy of spectrum along all propagation directions. However, up to certain range (distance), the signal strength is weak and possibly allow another co-existing transmission happening with a satisfactory signal to interference-and-noise ratio (SINR) at both transmit-receive (T-R) pairs. In this paper, we realize this concept for a CRN consisting of a primary (PR) T-R pair and a cognitive radio (CR) T-R pair; furthermore, we consider to what condition concurrent transmission can happen. We use the Lagrange multiplier method to determine the optimal power allocation scheme for such a CRN and then determine to what extent can the sum spectral efficiency be enhanced. It is found that the CR transmitter (CR-TX) may either transmit at its maximum allowable power or just turn off with no transmission power. Concurrent transmission of the PR T-R and CR T-R pairs with distance as a new dimension of multiplexing can be considered as a new version of CRN.

Improving FIR Filters by Using Cascade Techniques Tips & Tricks

High-performance filtering is the holy grail for all digital signal processing (DSP) practitioners. However, high-performance filtering is almost synonymous with high implementation complexity and, thus, high cost. This article focuses on designing high-performance finite impulse response (FIR) filters with less complexity. We present novel methods for improving the frequency response of an FIR filter by cascading it with complementary comb filters (CCFs). In particular, we redesign a low-order FIR filter by intentionally inducing a ripple at the passband edge and using CCFs of various lengths to compensate for the ripple. We use the zeros of CCFs to reshape the frequency response of the low-order FIR filter, subsequently called the prototype filter. Thus, the composite filter approaches an ideal lowpass filter (LPF) more closely in both the transition band and stopband. Because a CCF contains only one adder and a few storage units, the cost is minimal. The composite filter also maintains a linear phase response because all CCFs have linear phase responses. Through shifting the LPF response to high-frequency bands, we obtain highpass filters and bandpass filters (BPFs) by using the same methodology.