Soft Handover Research Articles

Time Coordinated V2I Communications and Handover for WAVE Networks

A wide variety of information technology (IT) services will become available for vehicles through the IEEE 802.11p, IEEE 1609, and wireless access in vehicular environment (WAVE) standards, and naturally the need for service handover will become a necessity. For WAVE networks, a time coordinated medium access control (MAC) protocol named WAVE point coordination function (WPCF) is proposed in this paper. The mathematical derivations and simulation analysis demonstrate that the proposed WPCF protocol can significantly enhance the utilization efficiency and can support more users based on an equal-length access period when compared to point coordination function (PCF), enhanced distributed channel access (EDCA), or hybrid coordination function (HCF) controlled channel access (HCCA) for vehicle to infrastructure (V2I) communications. The paper also demonstrates the effectiveness of the proposed WAVE handover controller (WHC) and WPCF in minimizing service disconnection time when used for V2I handover. In addition, technical enhancements and messages are added to enable seamless communication services over soft-handover (SHO), and enable minimum handover delay in hard-handover (HHO) situations. The mathematical performance evaluation and the simulation results show that the proposed scheme can significantly improve the handover latency compared to the performance that can be delivered by the current protocols.

Coverage planning for optimizing HSDPA performance and controlling R99 soft handover

Coverage planning is an important engineering task in deploying UMTS networks implementing both high speed downlink packet access (HSDPA) and Release 99 (R99) services. Coverage planning amounts to determining the cell coverage pattern by means of setting the common pilot channel (CPICH) power of the cells. A conventional strategy is to uniformly allocate a proportion of the total power to CPICH. In this paper, we develop mathematical modeling and optimization approaches to bring the benefit of power saving enabled by optimizing non-uniform CPICH to enhance HSDPA performance, while preserving a desired degree of soft handover (SHO) for R99. The study focuses on HSDPA performance at cell edges, where data throughput is typically low. An integer linear programming model is developed for the resulting optimization problem. The model admits optimal or near-optimal planning solutions for relatively small networks. Solution algorithms based on local search and repeated local search are developed. These algorithms are able to perform the optimization for large-scale networks time-efficiently. Experimental results for both synthesized networks as well as instances originating from real planning scenarios demonstrate the benefit of our optimization approach.

Soft handover mechanism based on RTP parallel transmission for mobile IPTV services

Mobile Internet Protocol Television (IPTV) provides users with multimedia content through wireless access technologies whenever they want and wherever they are. However, vertical handover in heterogeneous networks results in long interruption time and large packet loss rate, which poses a challenge for seamless mobile IPTV service. The existing solutions that make use of the heterogeneous access networks to transmit multimedia content have two drawbacks: high bandwidth consumption of the wireless networks and lots of packets loss when a user resides in the overlapped area of the boundary. To solve these issues, we propose a new soft handover mechanism, based on the IPTV server and the consumer electronic devices. The proposed Parallel Soft Handover (PSH) divides the Real-time Transport Protocol (RTP) packets according to the packet loss rates, and exploits different networks efficiently by using parallel transmission. Moreover, the selective retransmission for RTP packets is introduced to reduce the packet loss. Simulation results demonstrate that the PSH can reduce the packet loss rate, as well as obtain a more efficient use of the wireless bandwidth.

An Optimal Handover Decision for Throughput Enhancement

This letter proposes an optimal handover decision algorithm from the perspective of throughput enhancement. By considering two handover schemes (soft handover and fast cell selection), the proposed algorithm decides a handover only when a throughput gain exists. In order for this decision to be made, a new measurement parameter, Interference to other-Interferences-plus-Noise Ratio (IINR), is defined. The proposed IINR-based handover decision demonstrates optimal throughput performance, while the legacy signal to interference-plus-noise ratios (SINR)-based handover decision presents a tradeoff between throughput and feedback overhead.

Performance Enhancement of Cellular Network Using Adaptive Soft Handover Algorithm

Mobility management is the most important feature of a wireless cellular communication system. Continuation of an active call is one of the most important quality measurements in the cellular systems. Handover makes it possible for a user to travel between various networks or cells while having a seamless connection. This paper shows that, performance of cellular network can be increased with proposed adaptive soft handoff algorithm, which dynamically calculates the Soft handover margin based on the received signal strength and distance. Performance is evaluated in terms of the performance metrics active set update rate, active set size, soft handover region and probability of outage. Simulation results show that soft handover algorithm gives better performance with adaptive soft handoff margin compared to that of fixed soft handover margin in varied propagation conditions.

Investigation of Inter-Node B Macro Diversity for Single-Carrier Based Radio Access in Evolved UTRA Uplink

This paper investigates the gain of inter-Node B macro diversity for a scheduled-based shared channel using single-carrier FDMA radio access in the Evolved UTRA (UMTS Terrestrial Radio Access) uplink based on system-level simulations. More specifically, we clarify the gain of inter-Node B soft handover (SHO) with selection combining at the radio frame length level (=10msec) compared to that for hard handover (HHO) for a scheduled-based shared data channel, considering the gains of key packet-specific techniques including channel-dependent scheduling, adaptive modulation and coding (AMC), hybrid automatic repeat request (ARQ) with packet combining, and slow transmission power control (TPC). Simulation results show that the inter-Node B SHO increases the user throughput at the cell edge by approximately 10% for a short cell radius such as 100-300m due to the diversity gain from a sudden change in other-cell interference, which is a feature specific to full scheduled-based packet access. However, it is also shown that the gain of inter-Node B SHO compared to that for HHO is small in a macrocell environment when the cell radius is longer than approximately 500m due to the gains from hybrid ARQ with packet combining, slow TPC, and proportional fairness based channel-dependent scheduling.

A Hybrid Inter-Cell Interference Mitigation Scheme for an OFDMA Downlink System

A number of inter-cell interference coordination schemes have been proposed to mitigate the inter-cell interference problem for orthogonal frequency division multiple access (OFDMA) systems and among them, partial frequency reuse is considered one of the most promising approaches. In this paper, we propose an inter-cell interference mitigation scheme for an OFDMA downlink system, which makes use of both partial frequency reuse and soft handover. The basic idea of this hybrid scheme is to dynamically select between a partial frequency reuse scheme and a soft handover scheme to provide better signal quality for cell edge users. Compared with the standard partial frequency reuse scheme, simulation results show that approximately one quarter of cell edge users can get improvements in signal quality as well as link spectral efficiency from using the proposed hybrid scheme. We also observe that by using our approach, there is a significant cell edge throughput gain over the standard partial frequency reuse scheme. Furthermore, based on a well defined data rate fairness criterion, we show that our method achieves higher overall system capacity as compared with the standard partial frequency reuse scheme.

RTT Positioning Field Performance

The performance of cellular-positioning methods is characterized in terms of availability, response time, and accuracy. This paper discusses the measured field performance of Ericsson's round-trip time (RTT) positioning method in terms of the aforementioned parameters. The results are based on more than 1200 position fixes performed in a large commercial wideband code-division multiple-access (WCDMA) network. More than 100 surveyed test points were used, these being located in indoor, urban, suburban, and rural radio environments. Overviews of the RTT positioning algorithm, the test points, the test equipment, and the measurement procedures are given first. Then, this paper presents measurement geometries (for example, in soft handover), as well as the achieved performance in each radio environment. The radial distance accuracy was found to be excellent, despite the fact that propagation conditions were difficult with many open water surfaces. A bias of less than 5 m at the 50% point of the cumulative distribution function and a 95% error just above 150 m were obtained, averaged over all radio environments.

Avoiding Data Loss With Hard and Soft DVB-H Handovers

Digital Video Broadcasting-Handheld (DVB-H) allows the efficient transmission of rich multimedia services to small, handheld terminals. Such portable terminals pose specific requirements on the transmission technology, such as the need for seamless cell handover. This paper first presents mechanisms which allow loss-free hard handovers with DVB-H using only a single receiver front-end. It is then shown how even 3G-like soft handovers are possible with DVB-H, still using only a single receiver front-end. The proposed schemes are evaluated using simulations and field measurements.

SASHA—A Quality-Oriented Handover Algorithm for Multimedia Content Delivery to Mobile Users

The convergence of the existing network access technologies to a common IP-based architecture and the increase in popularity of accessing video content over the Internet makes IPTV a promising solution for media and entertainment industries. Additionally, video content delivery to the increasingly popular mobile devices over heterogeneous wireless networks makes IPTV even more appealing. However the distribution of multimedia content over heterogeneous wireless networks to mobile devices involves significant technical challenges related to mobility management and quality of service provisioning. The existing solutions do not consider quality of service as a decision making parameter for mobility management in general and handover management in particular. This paper proposes the smooth adaptive soft handover algorithm (SASHA), a novel quality-aware approach to handover based on load balancing among different networks using a comprehensive, quality of multimedia streaming (QMS), function for decision making. SASHA represents the handover management solution at the core of the more comprehensive multimedia mobility management system (M3S), a quality oriented mobility management framework for multimedia applications which maximizes user perceived quality by efficiently exploiting all available communication resources. Simulation-based testing results are presented, outlining the performance of SASHA in different mobility scenarios. The evaluation is performed for different number of nodes performing handover simultaneous and for various situations in terms of networks' overlapping area. The results shown indicate how SASHA outperforms other three mobility management solutions in terms of quality, scalability and resilience to the dynamics of the networks' overlapping area.

A New Soft Handover Mechanism using DCHs in 3GPP HSDPA Networks

In 3GPP (Third Generation Partnership Project) Release 5 (R5), HSDPA (High-Speed Downlink Packet Access) has been standardized to enhance the data rate of downlink packet transmission on top of WCDMA (Wideband Code Division Multiple Access) network. Even HSDPA supports up to 10 Mbps data rate through HSDSCHs (High Speed-Downlink Shared Channels), an UE (User Equipment) suffers from significant handover latency since HSDPA standard lacks supporting soft handover. Therefore, in this paper, we propose a new soft handover mechanism for HSDPA to reduce the handover latency by utilizing DCH (Dedicated Channel) instead of HS-DSCH. Simulation results show that the proposed soft handover mechanism reduces the packet IAT (Inter Arrival Time) less than 15 msec while HSDPA’s hard handover suffers from 190 msec packet IAT. It means that the proposed mechanism guarantees the minimum packet IAT requirement of the typical VoIP service in 20 msec. Furthermore, the proposed mechanism employees no service disruption for the data connection while an UE performs the soft handover procedure.

Semisoft Handover Gain Analysis Over OFDM-Based Broadband Systems

Various approaches to analyze handover have been developed to guarantee the quality of service of multimedia services over mobile communication networks. However, no framework for multicarrier-based broadband systems, e.g., multicarrier code-division multiple access and orthogonal frequency-division multiple access, is available based on the perspective of link capacity. This paper presents a handover technique referred to as semisoft-handover-utilizing macroscopic diversity, which permits both hard and soft handover advantages for services over multicarrier-based broadband networks to be retained. Theoretical analysis is then performed to measure the handover gain over the forward link in terms of an outage probability. Simulation data verify that semisoft handover outperforms other traditional handover techniques, in particular for high-data-rate services.

Finger management schemes for RAKE receivers with a minimum call drop criterion

We propose and analyze in this letter new finger management techniques which are applicable for RAKE receivers operating in the soft handover region. These schemes employ "distributed" types of generalized selection combining (GSC) and minimum selection GSC schemes in order to minimize the impact of sudden connection loss of one of the active base stations. By accurately quantifying the average error rate, we show through numerical examples that our newly proposed distributed schemes offer a clear advantage in comparison with their conventional counterparts.

Adaptive rake combining in the soft handover region

We propose and analyze new finger assignment schemes which are applicable for RAKE reception in the soft handover region. These schemes rely on variants of the conventional generalized selection combining (GSC) and the minimum selection GSC schemes in order to choose an acceptable base station and its corresponding paths. Relying on some recently derived results on order statistics, we investigate the average error rate performance as well as the average number of estimated and combined paths of the proposed schemes over independent and identically distributed Rayleigh fading channels. The mathematical formalism is illustrated with few selected numerical results that show the tradeoff between performance and processing power consumption.

Performance of Soft Handover Algorithm in Varied Propagation Environments

Performance of Soft Handover Algorithm in Varied Propagation Environments

Wireless Location Uses Geometrical Transformation Method With Single Propagation Delay: Model and Detection Performance

Inspired by recent promotions of wireless location services and applications, this paper develops a simple model for detecting a mobile caller location with low implementation complexity and promising accuracy. The model that is described in this paper employs the geometrical transformation method with single propagation delay measurement. Depending on the number of available surrounding base transceiver stations (BTSs), a set of the pseudodistances and pseudodistance differences is provided through the geometrical distances between the home and multiple foreign BTSs, which is called the geometrical transformation method. Accordingly, the mobile caller location can be detected using the circular location technique and the hyperbolic location technique. The major benefit of the proposed model is that during a call to detect the mobile caller's location, the use of geometrical transformation allows us to overcome the location handover problem. A forcing handover in a global system for mobile communications (GSM) network or a three-way soft handover in a universal mobile telecommunications system (UMTS) network, for example, occurs when detecting the location when a standard model that is based on the measurement of the propagation delay is utilized. Comparing the standard model with the proposed model, the former needs at least three propagation delays that were simultaneously measured from at least three BTSs, whereas the latter needs only a single propagation delay that was measured from the home BTS. Moreover, in the case where we do not have a priori information of a non-line-of-sight (NLOS) error, a deterministic parameter that is related to the propagation delay is defined. This parameter is shown as limited a priori information for calibrating the coarse resolution in the proposed location model, which is caused by the NLOS error. To have significant findings, we conduct a practical experiment in an urban environment based on a 1.8-GHz commercial cellular network. In the five-BTS case where the location error is less than 300 m, the probability of location error that the proposed model with a bit period of 1/2 achieved is greater than 0.85. Although the performance of the proposed location model does not satisfy the U.S. Federal Communications Commission Enhanced 911 (FCC E-911) requirements, it is a good solution for the deployment of wireless location services and applications.

MSIP: Extension of SIP for Soft Handover with Bicasting

This Letter proposes an extension of session initiation protocol (SIP) to support soft handover with bicasting, named mobile SIP (mSIP). In the mSIP scheme, the soft handover is achieved by bicasting to the mobile node in the handover region. For this purpose, a new handover' header is defined in the SIP re-INVITE message. The mSIP handover can reduce handover latency and loss, compared to the SIP handover.

Finger Replacement Schemes for RAKE Receivers in the Soft Handover Region With Multiple Base Stations

We propose and analyze new finger replacement techniques for RAKE reception in the soft handover (SHO) region with multiple base stations. The proposed schemes are basically based on the block comparison among groups of resolvable paths from different base stations and lead to the reduction of complexity while offering commensurate performance in comparison with previously proposed schemes. Relying on the newly derived analytical expressions, we investigate not only the complexity in terms of the average number of required path estimations/comparisons and the SHO overhead but the error performance of the proposed scheme over independent identically distributed (i.i.d.) fading channels as well. We also examine, via computer simulations, the effect of path unbalance/correlation as well as outdated/imperfect channel estimation and show the robustness of our proposed scheme to these practical limitations.

Uplink quality measurement reporting mechanism for HSUPA

This article proposes a new measurement reporting method applied for HSUPA systems. The presented mechanism offers an efficient uplink quality of service, especially in soft handover mobility conditions. 3GPP specifications restrict mobility procedures (such as serving cell change) to downlink quality measurement reporting. However, with the high data rate introduced on the uplink in HSUPA systems, downlink-only measurements can introduce reporting delays or mobility decision inaccuracies, and thus throughput degradation. The proposed algorithm provides event-based uplink measurements for the block error rate quality on each radio link in the HSUPA active set. Networks can then use the proposed mechanism along with the downlink event-based measurements to trigger a mobility procedure. The results show enhancements to the uplink throughput and overall system performance.

Intersystem Soft Handover for Converged DVB-H and UMTS Networks

Digital video broadcasting for handhelds (DVB-H) is the standard for broadcasting Internet Protocol (IP) data services to mobile portable devices. To provide interactive services for DVB-H, the Universal Mobile Telecommunications System (UMTS) can be used as a terrestrial interaction channel for the unidirectional DVB-H network. The converged DVB-H and UMTS network can be used to address the congestion problems due to the limited multimedia channel accesses of the UMTS network. In the converged network, intersystem soft handover between DVB-H and UMTS is needed for an optimum radio resource allocation, which reduces network operation cost while providing the required quality of service. This paper deals with the intersystem soft handover between DVB-H and UMTS in such a converged network. The converged network structure is presented. A novel soft handover scheme is proposed and evaluated. After considering the network operation cost, the performance tradeoff between the network quality of service and the network operation cost for the intersystem soft handover in the converged network is modeled using a stochastic tree and analyzed using a numerical simulation. The results show that the proposed algorithm is feasible and has the potential to be used for implementation in the real environment.