Improving the fault tolerance of GSM networks

A PCS network constantly tracks the locations of the mobile stations so that incoming calls can be delivered to the target mobile stations. In general, a two-level database system is used to store location information of the mobile stations. When the location databases fail, incoming calls may be lost. This article describes the standard GSM database failure restoration procedure which reduces the number of lost calls. Then we propose an efficient visitor location register (VLR) identification algorithm for the home location register (HLR) failure recovery procedure, which utilizes mobile station movement information to speed up the recovery procedure     

On the benefits of location-based relay selection in mobile wireless networks

We consider infrastructure-based mobile networks that are assisted by a single relay transmission where both the downstream destination and relay nodes are mobile. Selecting the optimal transmission path for a destination node requires up-to-date link quality estimates of all relevant links. If the relay selection is based on link quality measurements, the number of links to update grows quadratically with the number of nodes, and measurements need to be updated frequently when nodes are mobile. In this paper, we consider a location-based relay selection scheme where link qualities are estimated from node positions; in the scenario of a node-based location system such as GPS, the location-based approach reduces signaling overhead, which in this case only grows linearly with the number of nodes. This paper studies these two relay selection approaches and investigates how they are affected with varying information update interval, node mobility, location inaccuracy, and inaccurate propagation model parameters. Our results show that location-based relay selection performs better than SNR-based relay selection at typical levels of location error when medium-scale fading can be neglected or accurately predicted.     

Overflow control for cellular mobility database

In a cellular phone system, the service area is partitioned into several location areas (LAs). Every LA is associated with a mobility database called visitor location register (VLR). When a mobile user enters an LA, the user must register to the VLR before receiving any cellular service. If the VLR is full, the registration procedure fails and the system cannot deliver services to the user under the existing cellular technology. To resolve this problem, we propose a VLR overflow control scheme to accommodate the incoming mobile users during VLR overflow. Our scheme only requires minor modifications to the existing cellular mobility management protocols. Particularly, no modification is made to the mobile phones. An analytic model is proposed to investigate the performance of the overflow control scheme. When exercising the scheme, the call setup procedure for an “overflow” user is more expensive than that for a “normal” user. Under the range of input parameters considered in our study, we show that even if the VLR overflow situation is serious, the overhead for exercising the overflow control scheme is very low     

A novel feedback scheme to increase throughput in multiple access radio systems

To enhance the throughput of a slotted ALOHA control channel in a radio communication system, we present and analyze a method for estimating the number of remote stations that are attempting to transmit to a central base station. Each of the contending remote stations randomly chooses to transmit with probability p. Our novel contribution is the use of information concerning the number of successful packet transmissions that arrive without retransmission (i.e., that are successfully received on their first transmission attempt), as a metric for accurately and robustly estimating the number of contending remote stations. This estimate is determined at the base station and then used to compute the optimal transmission probability p that is used as feedback to the remote stations for their use. The proposed estimation method is analyzed and shown to provide good steady‐state performance for a variety of system models, including situations with noise and idling remote stations. The scheme is also shown to provide good tracking capabilities. This revised version was published online in August 2006 with corrections to the Cover Date.     

Two-level pointer forwarding strategy for location management in PCS networks

For a IPCS network to effectively deliver services to its mobile users, it must have an efficient way to keep track of the mobile users. The location management fulfills this task through location registration and paging. To reduce the signaling traffic, many schemes such as a local anchor (LA) scheme, per-user caching scheme and pointer forwarding scheme have been proposed in the past. In this paper, we present a new location management scheme which intends to mitigate the signaling traffic as well as reduce the tracking delay in the PCS systems. In this strategy, we choose a set of visitor location registers (VLRs) traversed by users as the mobility agents (MA), which form another level of management in order to make some registration signaling traffic localized. The idea is as follows: instead of always updating to the home location register (HLR), which would become the bottleneck otherwise, many location updates are carried out in the mobility agents. Thus, the two-level pointer forwarding scheme is designed to reduce the signaling traffic: pointers can be set up between VLRs as the traditional pointer forwarding scheme and can also be set up between MAs. The numerical results show that this strategy can significantly reduce the network signaling traffic for users with low CMR without increasing much of the call setup delay.     

Performance analysis of bandwidth requests under unicast, multicast and broadcast pollings in IEEE 802.16d/e

In the polling mode in IEEE 802.16d/e, one of three modes: unicast, multicast and broadcast pollings, is used to reserve bandwidth for data transmission. In the unicast polling, the BS polls each individual MS to allow to transmit a bandwidth request packet, while in the multicast and broadcast pollings, the truncated binary exponential backoff (TBEB) mechanism is adopted as a contention resolution among mobile stations (MSs) in a multicast or broadcast group. This paper investigates the delay of bandwidth requests in the unicast, multicast and broadcast pollings, by deriving the delay distribution of the unicast polling and the TBEB by means of analytical methods. We consider an error-free channel as well as an error-prone channel with i.i.d. constant packet error rate per frame. Furthermore, we find the utilization of transmission opportunity to see efficiency of the bandwidth in the TBEB. Performance evaluations are provided to show that analytical results are well-matched with simulations. By the numerical results, we can find the optimal parameters such as the initial backoff window size of the TBEB and the number of transmission opportunities (or slots) satisfying quality of service (QoS) requirement on delay and loss, and thus we can determine which scheme is better than others depending on the probability of a request arrival during one frame. Numerical examples address that the TBEB performs better than the unicast polling for light traffic loads and vice versa for heavy traffic loads. Also, it is shown that the multicast polling has better performance than the broadcast polling in the sense of shorter delay, lower loss probability and higher utilization of transmission opportunity.     

Generic stationary backoff distributions for distributed multiple access control

In this paper, we study the characteristics of two different backoff schemes: one that maximizes the channel utilization and one that maximizes the probability of a successful transmission. Our results indicate that while the latter provides slightly lower channel utilization, its shape is much less sensitive to the number of contending nodes. That is, the channel utilization is kept almost constant for a very wide range of node densities if the backoff distribution has increasing shape. This motivates us to propose a simple heuristic backoff scheme called the Truncated Geometric Backoff Distribution (TGBD). We provide simple analytical expressions for the probability of a successful transmission and the channel utilization. We also show that the TGBD can easily be extended to support service differentiation by adjusting the window lengths, and we provide a simple approximation that gives the relative share of the capacity for a node in a priority class compared to nodes in other classes. This extended backoff scheme easily outperforms the much more complex Quality of Service (QoS) standard, IEEE802.11e EDCA. Finally, a two-stage backoff model, based on the TGBD, is proposed that further increases the probability of a successful transmission. Results indicate that the channel utilization is almost independent of the number of contending nodes.     

Bandwidth-reservation scheme based on road information for next-generation cellular networks

Channel-reservation techniques have been widely studied in cellular networks in order to meet the desired quality-of-service requirements. In this paper, a distributed predictive channel-reservation scheme, called the road-map-based channel-reservation scheme (RMCR), and a call-admission-control algorithm are proposed. The goal is to reduce the handoff-dropping probability and to improve the bandwidth utilization. In the RMCR scheme, we assume that base stations (BSs) are equipped with road-map information and that mobile stations (MSs) are equipped with global positioning systems (GPS) devices. MSs periodically report their GPS location information to their BSs. Based on the location information of the MSs at two consecutive epochs, the BSs estimate the speed and moving direction of the MSs. Furthermore, the BSs estimate the probability that the MSs will enter the neighboring cells based on their velocity and the road-map information stored in the BSs. The BSs then compute the amount of bandwidth to be reserved, based on such estimation. With the road-map information, the BSs can make a more-accurate prediction on the user's mobility and, hence, reduce unnecessary bandwidth reservation. Simulation results show that RMCR is capable of keeping the handoff-dropping probability low and allocating bandwidth to new/handoff calls efficiently. We also show that RMCR is robust with respect to system parameters such as user's speed, the density of roads, the accuracy of mobility measurement, and so on.     

Design of optimal relay location in two-hop cellular systems

Relay stations are usually used to enhance the signal strength for the users near cell boundary, thereby extending the cell coverage. However, transmission through a relay station needs two transmission phases. The first phase is from base station to relay station, and the second one is from relay station to mobile station. Thus, using relay station may decrease system capacity due to two-phase transmission time. As a result, whether or not data are transmitted by one-hop or two-hop phases should be determined according to both signal strength and throughput. In this paper, we investigate the optimal relay location aiming to maximize system capacity. We consider two relay selection rules for determining whether two-hop transmission will be used: signal strength-oriented and throughput-oriented selection rules. We find that the signal strength-oriented two-hop transmission may yield even lower system capacity than the one-hop transmission. In the throughput-oriented scheme, the two-hop transmission can achieve higher system capacity than the one-hop transmission. By simulations, we determine the optimal relay location and show the coverage enhancement by the relaying network. Extensive simulations are performed to investigate the impacts of relay transmission power and the number of relay stations on system capacity and optimal relay location. The simulation results reveal important insights into designing a relaying network with high system capacity.     

Local anchor scheme for reducing signaling costs in personalcommunications networks

A personal communications network (PCN) location tracking scheme called local anchoring is introduced which reduces the signalling cost as compared to the location management strategy proposed in the IS-41 standard. Local anchoring reduces the number of location registration messages between the home location register (HLR) and the visitor location registers (VLRs) in a way that location change is reported to a nearby VLR called the local anchor (LA) instead of to the HLR. This method successfully reduces the cost for location tracking when the call arrival rate is low relative to the mobility rate and the cost for location registration is high. A dynamic local anchoring mechanism is then introduced which dynamically selects the LA such that the expected cost for location registration and call delivery can be further reduced. It is demonstrated that the cost of dynamic local anchoring is always lower than or equal to that of the IS-41 scheme     

Group location tracking based on representative identity andvirtual VLR for transportation systems

A location tracking scheme known as group location tracking (GLT) is proposed to reduce the location update cost for terrestrial transportation systems (TSs) in personal communication networks. When a TS moves into a new registration area, the GLT scheme, based on a representative identity of the TS and a virtual visitor location register, updates location information by a group location update request message instead of individual location update of users. Compared with the IS-41, the GLT scheme significantly reduces signaling load     

D2D辅助的窄带物联网中能耗和传输成功率的最优折中

在设备到设备(D2D)通信辅助的窄带物联网(NB-IoT)中,为了尽可能提高传输成功率,D2D接收端需要预留较多的通信时隙(可以允许多次重传)。然而,这显著地增加了用户设备(UE)的能耗,特别是在信道条件较差或者相邻D2D链路干扰较严重的情况下。该文基于中继和能耗模型构造了一个传输成功率和能耗折中的优化问题,进而提出一个基于二分法的通信时隙最优配置算法。数值结果表明较多的预留时隙数量极大地增加了UE的能耗,但是不会显著提高传输成功率,与多中继传输、随机中继传输和100%成功传输等其他算法相比,该文提出的预留时隙最优配置算法获得了最小的能耗和几乎最大的传输成功率(只比100%成功传输方案低)。     

An adaptive p-persistent MAC scheme for multimedia WLAN

The letter proposes an adaptive p-persistent-based (APP) medium access control (MAC) scheme for the IEEE 802.11e distributed WLAN supporting multimedia services. The APP MAC scheme adaptively gives differentiated permission probabilities to transmission stations which are in different access category and with various waiting delay. Simulation results show that the APP MAC scheme can improve the performance of multimedia WLAN, such as small voice packet dropping probability, low delay variation, and high system throughput, compared to conventional MAC algorithms     

Intelligent cruise control and reliable communication of mobilestations

The reliability of a short range packet radio network for mobile stations is investigated via the probability of a successful transmission. The instantaneous power of an interfering station's transmission is described by a Rayleigh distribution. The authors determine the distribution of cumulated interference power and the probability of a successful transmission, when the number of interfering stations is random and each station transmits only with probability p. Two lower bounds of increasing complexity are given. The authors evaluate these bounds for an intelligent cruise control system, when mobile stations are lined up in a traffic jam, and one approaching vehicle should be warned by the last member of the queue     

Dynamic hierarchical database architecture for location managementin PCS networks

This paper introduces a dynamic hierarchical database architecture for location management in personal communications service (PCS) networks. The proposed scheme allows the dynamic adjustments of user location information distribution based on the mobility and calling patterns of the mobile terminals (MTs). A unique distribution strategy is determined for each MT, and location pointers are set up at selected remote locations which indicate the current location of the MTs. This method effectively reduces the signaling and database access overhead for location registration and call delivery. Besides, the required processing is handled by a distributed network of directory registers and centralized coordination is not necessary. The functions of the other network elements, such as the home location register (HLR) and the visitor location registers (VLRs), remain primarily unchanged. This greatly facilitates the deployment of this scheme in current PCS networks     

Performance analysis of hexagonal cellular networks in fading channels

This paper analyzes the location‐dependent performance metrics of coverage probability and spectral efficiency in hexagonal cellular networks under Rayleigh fading with a general distribution for shadowing and also including two special cases of no shadowing and lognormal shadowing. The effects of system parameters such as frequency reuse factor, transmission probability of base stations, and signal‐to‐interference‐plus‐noise ratio gap from Shannon capacity are accurately characterized. The proposed approach is applied to fractional frequency reuse (FFR) scheme where the impact of FFR on spectral efficiency is evaluated. Numerical results show that (i) in a lognormal‐shadowed Rayleigh fading channel with the shadowing standard deviation of 12 dB, the cell area wide spectral efficiency is degraded by approximately 40% compared with when there is Rayleigh fading without shadowing; (ii) the improvement in spectral efficiency achieved by FFR over the universal frequency reuse increases as the transmission probability increases and the shadowing becomes less severe; and (iii) in Rayleigh fading without shadowing environment where all the base stations are actively transmitting, FFR achieves approximately 20% improvement in spectral efficiency in the cell edge area. Interestingly, this improvement increases to about 30% if a 3‐dB signal‐to‐interference‐plus‐noise ratio gap from Shannon capacity is further accounted. Copyright © 2015 JohnWiley & Sons     

Determination of the Registration Point for Location Update by Dynamic Programming in PCS

Location management is important to effectively keep track of mobile terminals with reduced signal flows and database queries. Even though dynamic location management strategies are known to show good performance, we in this paper consider the static location management strategy which is easy to implement. A system with single home location register and pointer forwarding is assumed. A mobile terminal is assumed to have memory to store the IDs of visitor location registers (VLRs) each of which has the forwarding pointer to identify its current location. To obtain the registration point which minimizes the database access and signaling cost from the current time to the time of power-off probabilistic dynamic programming formulation is presented. A Selective Pointer Forwarding scheme is proposed which is based on one-step dynamic programming. The proposed location update scheme determines the least cost temporary VLR which point forwards the latest location of the mobile. The computational results show that the proposed scheme outperforms IS-41, pure Pointer Forwarding, and One-step Pointer Forwarding at the expense of small storage and a few computations at the mobile terminals.     

Group location management for mobile subscribers on transportation systems in mobile communication networks

We propose a new location tracking scheme for subscribers on transportation systems (TSs) in which a large number of fast-moving users have the same location as the TS. The group location tracking (GLT) scheme in which a group location update is performed instead of the IS-41's individual location update has been proposed. We propose a distributed GLT (DGLT) scheme based on several virtual visitor location registers (VVLRs) and representative identities. We analyze the GLT and DGLT schemes in view of the database (DB) access cost as well as the signaling cost under one-dimensional network architecture. Compared with the IS-41 scheme, the schemes based on group management generally have a lower signaling cost and a lower DB access cost due to a significant reduction in the number of location updates. As user mobility increases or the number of users on a TS increases, the performance of the group management schemes improves. The DGLT scheme, in which a corresponding home location register selects a closest VVLR among several possible VVLRs, generally has a lower signaling cost although a DB access cost is increased slightly compared with the GLT scheme. We also obtain the regions in which the DGLT is more efficient than the IS-41 and the GLT scheme. The DGLT scheme is an appropriate solution for high signaling cost systems and the GLT scheme is useful for high DB access cost systems.     

A call admission control scheme for packet data in CDMA cellular communications

In wireless cellular communication systems, call admission control (CAC) is to ensure satisfactory services for mobile users and maximize the utilization of the limited radio spectrum. In this paper, we propose a new CAC scheme for a code division multiple access (CDMA) wireless cellular network supporting heterogeneous self-similar data traffic. In addition to ensuring transmission accuracy at the bit level, the CAC scheme guarantees service requirements at both the call level and the packet level. The grade of service (GoS) at the call level and the quality of service (QoS) at the packet level are evaluated using the handoff call dropping probability and the packet transmission delay, respectively. The effective bandwidth approach for data traffic is applied to guarantee QoS requirements. Handoff probability and cell overload probability are derived via the traffic aggregation method. The two probabilities are used to determine the handoff call dropping probability, and the GoS requirement can be guaranteed on a per call basis. Numerical analysis and computer simulation results demonstrate that the proposed CAC scheme can meet both QoS and GoS requirements and achieve efficient resource utilization.     

基于测向定位的算法研究

讨论了测向定位中的若干实际问题，包括两站、三站和多站交会定位的情况。利用示向度均值和方差、示向线交叉角、示向度质量等参数作为因子，分别给出了最佳交会点估计求解式，并对交会点的位置进行了误差分析。在实际工程使用中，本文给出的算法具有相当的实用性，定位精度显著提高。