Performance Analysis of Trunk Network for Inter-MSC Soft Handoffs in CDMA Cellular Communication Systems

Code division multiple access (CDMA)-based radio-on-fiber road-vehicle communication systems were proposed to support real-time streaming services in intelligent transportation systems (ITSs). Soft handoff should be provided for real-time streaming services because these services are required to guarantee real-time property and quality of service (QoS). However, soft handoff of real-time streaming services causes the shortage of resource in view of the system. In this paper, the double-adjustment soft-handoff (DASH) scheme is proposed to support seamless service regardless of the shortage of resource and maximize the resource efficiency when real-time streaming services are served in CDMA-based ITSs. The DASH scheme adjusts the data rate of a call when it starts and finishes soft handoff. The performance of the DASH scheme is evaluated by analytical and simulation methods. Performances are evaluated with respect to the blocking probability, the handoff failure probability, and the carried traffic. Numerical results show that the proposed scheme can give relative good maintenance of calls and good throughput.

CDMA (code division multiple access) is a promising air interface technique for digital cellular systems. The soft handoff between base stations is one of many important features of CDMA for the mobile station crossing the cell boundaries. When a mobile station during a call moves to an adjacent MSC (mobile switching center) service area, we propose that the traffic data from the new base station be carried to the old MSC through the link between MSCs. The old MSC receives multiple traffic data from the base stations that are serving the mobile station requesting the inter-MSC soft handoff. We develop an analytical approach for calculating the traffic load on the link by the soft handoffs between MSCs. The service area of an MSC is defined as the union of the service areas of the base stations and is assumed to have a hexagonal shape. The blocking probability of the soft handoff between MSCs due to the shortage of the link capacity is derived by the Erlang loss formula.

Existing soft handoff techniques lead to plenty of out-of- sequence packets during downward vertical handoffs (DVHOs). In this paper, we present two new network-layer soft vertical handoff schemes, called SHORDER and E-SHORDER. The former can prevent mobile nodes from receiving reordered packets during DVHOs with a low overhead. The latter further hinders their correspondent nodes from receiving out-of-order packets caused by mobile nodes' DVHOs. Then, we analyze the performance of our proposed approaches. By experiments, we show that they have a good effect in practice.

Soft handoff techniques are generally used in the downlink of CDMA cellular systems. When there is traffic deviation, the communications quality differs between cells. Some methods of equalizing the quality, such as signal-to-interference ratio (SIR)-based power control methods and flexible cell control methods have been developed. The method described in this paper controls the transmission power ratio allocated to the mobile stations in a soft handoff region according to the traffic load. The SIR difference between cells can be reduced by controlling the power transmitted to the soft handoff mobile stations. We calculate an optimum power allocation ratio for minimizing the SIR difference for a given traffic deviation range and the downlink orthogonality factor.

In code division multiple access mobile cellular networks, the transmission quality can be improved by using the soft handoff techniques. The present investigation is concerned with the admission control policies by exploiting the soft handoff coverage area of the cellular radio network. We suggest finite Markov models for the admission control based on reserve channel and sub-rating policies. In reserve channel policy, a fixed number of channels are reserved exclusively to serve the handoff calls whereas according to sub-rating policy, the occupied channels can be split into two half rate channels to accommodate more handoff voice calls. It is also considered that the new call generation rate per unit area is uniformly distributed over the service area. Various performance indices are derived in terms of steady state probabilities. For some special situations, we validate and compare the models developed with previous existing models by setting the system descriptors. To examine the effect of various parameters on the performance measures, the sensitivity analysis is carried out by taking illustrations.

The capacity of CDMA systems is determined by the number of channel elements (CE) or the amount of interference. Cell overloading may arise due to CE shortage in spite of low interference. We propose an improved soft handoff control which solves the cell overloading by contracting the soft handoff region. The extent of the handoff region contraction is determined by considering the amount of adjacent-cell interference and the extent of traffic congestion simultaneously.

Traffic nonuniformity degrades the performance of CDMA cellular systems. The authors present a new algorithm called the variable threshold soft handoff (VTSH) which reduces the performance degradation due to traffic nonuniformity in CDMA cellular systems. Unlike the conventional fixed handoff thresholds, the proposed algorithm allows the handoff thresholds (T ADD and T DROP) to vary dynamically according to the traffic density of each cell. This algorithm has been implemented by means of computer simulation and the results show that VTSH improves the overall CDMA system performance in terms of outage probability. The VTSH algorithm can easily be applied to CDMA cellular systems without any modification.

In cellular systems, due to the mobility, proper handoff or handover management is critical to ensure seamless migration from one cell to another cell. Besides of maintaining the connection quality during a handover process, any advanced handover algorithms which can minimize required resources for the connection are critical. In 2G, 3G, and future wireless systems, to maintain the best connection quality, fast switching and soft handoff are considered for high transmission performance. To achieve fast-switching or soft handoff, multiple sectors/cells are required to be activated prior to the actual connection. As a result, extra resources from cells/sectors are needed to support the connection. Algorithms which can effectively minimize active sector/cell set without affecting connection quality is important to reduce the required hardware and RF resources. In this paper, considering handoff controls for the same cellular system, we will review the development of related critical patents. Even those patents are originally designed for CDMA cellular systems, the control concepts can also apply to recent OFDMA based systems like WiMAX and 4G cellular systems. Keywords: Handoff, handover, CDMA, WIMAX, OFDMA, pilot, slope, cellular system, mobility

Soft handoff (SHO) is one of the critical components that determine the performance of a CDMA cellular system. The mobile station in 3G systems send power control commands to the base stations to adjust their powers. These power control commands can be received in error by on of the base stations in the active set serving the mobile. This results in the base stations transmitted powers deviating. Reducing the deviation in the base stations transmitted powers helps to achieve the desired diversity gain from SHO. We propose to change the way the base stations respond to power control commands. This does not require changing the way the mobile issues the power control commands. From the simulation results we see that at a speed of 5 km/h, the probability that the difference in the two base stations transmitted powers being greater than 5 dB is about 25% using the conventional scheme while it is only 8% for the proposed scheme (majority voting over two commands). We notice also that the base stations average transmitted power is reduced by employing the majority voting scheme.

Power control is an essential radio resource management method in CDMA cellular communication systems, where co-channel and adjacent-channel interferences are the primary capacity limiting factors. Power control intends to control the transmission power levels in such a way that required quality of service for the users is guaranteed with lowest possible transmission powers. In this paper, a modulation of power control algorithm is proposed for the 3G WCDMA system. The algorithm is figured on a modification of the transmitted power update step size. Instead of the fixed value presently suggested, the step size is modified dynamically in order to obtain more adapted power variations as well as the step is also represented as a function of the difference between the target and estimated SIR of the MS to obtain more stability of the system. A general form of this algorithm is presented and it is then studied in a simple simulation. Performance of the algorithm was evaluated with the outage percentage, which is the percentage of the number of MS's whose received SIR falls below the fixed threshold. The focused requirement, which had been tried to achieve by this algorithm, is the stability, which was studied and represented through simulation.

The traffic performance of integrated 3G wide-band code division multiple access (WCDMA) and GSM/GPRS network is evaluated. This type of network links two cellular radio systems which have different set of frequency bands and the same coverage size. The base station of 3G WCDMA is installed on an existing GSM/GPRS site. Dual-mode mobile terminals use handoff to establish calls on the better system. The soft handoff or inter-frequency hard handoff occurs when mobile terminals of 3G WCDMA or GSM/GPRS move between two adjacent cells, respectively. The inter-system hard handoffs are used between 3G WCDMA and GSM/GPRS systems. The data rate conversions between different systems, soft handoff region size, multiple data rate multimedia services, and the effect of the mobile terminal mobility on the user mean dwell time in each system are considered in the study. The simulation results demonstrate that a great traffic performance improvement on the complementary use of 3G WCDMA and GSM/GPRS cellular radio networks compared with the use of GSM/GPRS cellular radio networks. When high-data rate transmission is chosen for low-mobility subscribers, both the handoff failure probability, and carried traffic rates increase with the new call generation rate. However, both rates decrease conversely with the increasing new call generation rate as soon as the new call generation rate exceeds a critical value. This causes the integrated networks saturation. The higher mean speed for the mobile terminals produces lower new call blocking probabilities and total carried traffic. The new call blocking probabilities and total carried traffic increase with the size of the soft handoff region.

The transmitted data rate over the forward traffic channel in the existing CDMA cellular communication system and the proposed next generation CDMA cellular communication systems is variable from frame to frame. In order to reduce the frame overhead, however, the data rate information is not provided in the transmitted frame data. This paper presents the optimal frame rate detection scheme in the sense of minimizing the frame rate detection error probability in the AWGN channel. Simulation results show that the proposed rate detection scheme can provide a gain of up to 4.4 dB over the conventional method in terms of the required bit energy to noise ratio E/sub b//N/sub 0/ at a detection error rate of 10/sup -4/ in the AWGN environment.

Code-division multiple-access (CDMA) cellular systems use soft handoff. Although the capacity of CDMA systems is interference-limited in nature, channel shortages may occur because soft handoff uses several channels simultaneously. To cope with this problem, we propose an improved handoff method that borrows channels from stationary calls participating in soft handoff and allocates the borrowed channels to handoff requests by moving calls when a channel shortage occurs. Borrowing from stationary calls is possible because these calls do not undergo fast-fading and do not require receiver diversity. The proposed method is designed to avoid increased interference resulting from channel borrowing. The proposed channel-burrowing handoff scheme is analyzed in a situation involving both moving and stationary calls. A comparison is made between the performances of the typical IS-95-based handoff scheme and the proposed scheme. Numerical results show that the proposed scheme is better than the IS-95 scheme in view of the handoff refused probability, the handoff queuing delay, and total interference.

With the integration of heterogeneous wireless technologies and the popularization of all-IP networks,network-layer soft handoff approaches have gradually evolved to improve the performance of vertical handoffs(VHOs).Unfortunately,the existing soft handoff approaches lead to plenty of out-of-order packets during downward VHOs.In this paper,the authors present a new network-layer soft vertical handoff scheme,called SHORDER.In the scheme,the mobile node(MN)starts or stops buffering packets from its new network based on a few interactive messages with its home agent(HA).With the buffering technique,the scheme can prevent mobile terminals from receiving reordered packets caused by downward VHOs,and is compatible with various transport-layer protocols and their variants due to its independence.Then,the authors theoretically analyze the influence of the proposed scheme on the handoff latency,the goodput and the congestion window of the TCP in comparison with a typical existing network-layer soft VHO method.Additionally,the authors also derive the applicable condition of the SHORDER scheme.Experiments show that the deployment of the proposed scheme is easy and the scheme has better performance under its applicable condition,further,experimental and analytical results are consistent with each other.Finally,based on the applicable condition of the SHORDER scheme,the scheme further is improved.

A new call admission control (CAC) strategy based on the soft capacity constraint (SCC) concept is proposed for CDMA cellular systems. The use of the SCC concept allows maximizing system capacity while at the same time meeting the quality of service (QoS) requirements in terms of the outage probability. The fractional channel reservation (FCR) scheme is also used in the proposed CAC strategy as a system capacity booster. The proposed CAC strategy is mathematically analyzed by means of a teletraffic analysis considering both soft handoff and users' mobility. Realistic mobility conditions are taken into account by characterizing users' mobility parameters considering a smooth random mobility model. Novel mathematical expressions for the new call blocking, handoff failure, and forced termination probabilities are then derived. Mason's rule is employed for the derivation of the forced termination probability.