Tzu-Ming Lin

PRADA: Prioritized Random Access With Dynamic Access Barring for MTC in 3GPP LTE-A Networks

Due to the huge amount of machine-type communications (MTC) devices, radio access network (RAN) overload is a critical issue in cellular-based MTC. The prioritized random access with dynamic access barring (PRADA) framework was proposed to efficiently tackle the RAN overload problem and provide quality of service (QoS) for different classes of MTC devices in Third-Generation Partnership Project (3GPP) Long-Term Evolution Advanced (LTE-A) networks. The RAN overload issue is solved by preallocating random access channel (RACH) resources for different MTC classes with class-dependent back-off procedures and preventing a large number of simultaneous random access requests using dynamic access barring. In this paper, the performances of LTE-A without access barring, extended access barring (EAB), and PRADA are mathematically derived and compared, showing the superior performance of the PRADA scheme.

An Enhanced Handover Scheme for Mobile Relays in LTE-A High-Speed Rail Networks

Recently, the mobile relay technique has been discussed to support communication services for Long-Term Evolution Advanced (LTE-A) high-speed rail networks. In the network, there are several mobile relays in a train. User equipment (UE) devices connect to in-car mobile relays instead of outside evolved NodeBs (eNBs). Mobile relays establish backhaul links with the serving donor eNBs (DeNBs) and coordinate control and data flows for UE devices. Since the train travels in high speed, mobile relays suffer from frequent handovers between DeNBs. We observe that the defined handover procedures in LTE-A specifications may incur message overhead and lengthen handover time. In this paper, we propose an enhanced handover scheme, which contains two procedures. The first procedure is an enhanced measurement procedure, which can accelerate the measurement procedure when the mobile relay knows that the train is moving toward some neighbor DeNBs. The second procedure is a group in-network handover procedure, which can aggregate similar in network handover procedures in the core network. Performance evaluations indicate that our design can conserve both time and messages when handover.

Energy conserving packet transmission schemes for video and voice over WLAN

The design of packet transmission mechanisms of video and voice over wireless networks generally utilizes the characteristics of real-time data to improve the network performance, the energy efficiency of mobile devices, and etc. Unfortunately, WLAN medium access control (MAC) layer does not distinguish real-time and data packets during MAC frame transmission, and this design introduces network overheads and extra power consumption of video and voice over WLAN (V 2 oWLAN) stations (STAs). In this paper, we propose a transmission scheme to eliminate WLAN MAC acknowledgment frames of real-time packets dynamically in order to reduce the power consumption of V 2 oWLAN STAs and to improve the network utilization without sacrificing video and voice qualities. The proposed transmission scheme utilizes the WLAN multicasting method that does not require MAC acknowledgment, and the method thus can be implemented on the existing WLAN infrastructures by only software upgrades. Simulation results demonstrate that the proposed scheme improves the network utilization and the energy efficiency of V 2 oWLAN applications.

An Efficient Automatic Repeat Request Mechanism for Wireless Multihop Relay Networks

Recently, relay technology has been adopted to enhance the coverage and performance of wireless networks such as Worldwide Interoperability for Microwave Access and Long-Term Evolution Advanced (LTE-A). However, using relays to forward packets may induce more packet losses than traditional single-hop wireless networks because transmissions are conducted through multiple radio links. When there are lost packets, relay stations (RSs) decide whether to retransmit these packets with automatic repeat request (ARQ) strategies. We observe that an improper ARQ strategy increases latency, blocked packets, and workloads on the multihop relay network. This paper proposes a new relay ARQ (RARQ) scheme, providing efficient acknowledgement to reduce packet latency and the number of blocked packets with small workloads. We also propose an analytic model to evaluate the performance of the proposed mechanism. Simulation results have validated the proposed model and demonstrated that our ARQ scheme outperforms conventional approaches.

Non-orthogonal direct access for small data transmission in cellular MTC networks

In conventional LTE networks, user equipments (UEs) access the network via a four-step random access procedure. When small amount of data is transmitted, such as in the scenarios of machine-type communications (MTC), signaling overhead resulted from the random access procedure becomes a critical issue. To enable an efficient small data transmission, a direct access scheme utilizing code division multiplexing (CDM) is proposed in this paper. Instead of transmitting on the resource blocks indicated by eNB, UEs randomly select resource blocks for direct data transmission without signaling eNB, with CDM used to resolve the collision problem. Under the proposed architecture, however, the data transmission is inherently non-orthogonal and the eNB has to detect the data without any information from UEs, making the receiver too complex to implement. To ease the burden of the receiver, we design a pseudo-random resource selection scheme such that the search space of the data detection is reduced. The analysis and simulation results show the advantage of using the proposed direct access scheme to improve the efficiency of small data transmission in cellular networks.

Data Forwarding in Wireless Relay Networks

Broadband wireless communication has brought users a number of multimedia services for years. As wireless broadband markets mature, system operators face new problems. First, system capacity is bounded by finite radio resources. Second, service providers increasing spend on network deployments and services provisions. With limited radio resource and increased costs, operators have no choice but to force users to pay higher rates to preserve the same service quality than they had several years ago. The expectation is that these problems are solved by introducing relay station (RS) into traditional wireless systems. The relaying technology has proven to be a feasible technology to expand system capacity and reduce deployment costs simultaneously. One of the most popular technologies is cooperative communications that boost network throughput significantly by improving the radio quality for transmission and reception (Nosratinia et al., 2004); (Mohr, 2005); (Doppler et al., 2007). Numerical results (Soldani & Dixit, 2008) showed the cost saving benefits when conventional communication networks adopt relay functionality. From this, a commercial cellular system can save more than 56 % on capital expenditures when RSs are deployed. RS is a wireless communication station that provides relay services for receiving and forwarding radio signals between two stations. In a cellular system, RS is in charge of receiving, decoding, and forwarding data between the Base Station (BS) and the Subscriber Stations (SSs). During the relaying, RS provides additional features to assist data transmissions. For example, (Tao et al., 2007) proposed a novel data forwarding scheme in this environment. The novel data forwarding scheme improved the transmission efficiency by approximately 66 %. Although data relay shows superior performances in throughput enhancements and cost savings. Multi-hop relaying introduces new issues that impact overall performance. To indicate a routing path in multi-hop circumstances, additional control information should be introduced. The routing indication design for multiple radio links introduces new overhead and may impact transmission efficiency during relay. Imprecise indications may waste RS computation and storage since it does not know what it shall relay and where to forward. Moreover, there may be a case that data destined to others are received by the RS that is not in charge. Imprecise relay indication will not only increase overheads but also lead RS to use its processor and storage inefficiently. In other words, data forwarding with ambiguous control information would increase RS complexity and buffer storage unnecessarily. During

A Simple and Efficient Data Forwarding Mechanism In Wireless Relay Networks

Wireless relay network is a low-cost solution for extending the service coverage and increasing the throughput of the conventional single-hop wireless network. By deploying a relay network, a base station (BS) can provide services to subscriber stations (SSs) through relay links. The functionality of a relay station (RS) is simpler than a BS, and RSs only forward packets between SSs, RSs and the BS without too much packet processing. However, current solutions require a RS to store and process the packet before it can determine the destination, and thus introduce extra processing and buffering overheads on the RS. This study proposes a simple and efficient forwarding scheme which multiplexes bursts to the SSs attached to the same access RS. By applying the proposed end-to-end burst switching mechanism, the RS merely checks the frame header and can decide the final destination without packet processing. The experiment results demonstrate the superior performance of the proposed scheme than other approaches.