5G网络上行覆盖增强研究

当前5G网络频段多为高频段,带宽资源丰富,但路径损耗、穿透损耗较高,上行覆盖相对较弱,如果引入低频段资源进行上行传输,高、低频载波协同有助于提升上行覆盖。结合频谱特性及行业现状,分析2.1 GHz和3.5 GHz等频段的链路预算和覆盖性能,比较上行覆盖增强的3种方案,并对载波聚合方案的优势和限制进行了具体分析,结果表明载波聚合方案是5G网络上行覆盖增强的优化解决方案。     

System design of cdma2000 femtocells - [femtocell wireless communications]

Femtocells extend the cellular network coverage and provide high speed data service inside homes and enterprises for mobiles supporting existing cellular radio communication techniques. They also provide additional system capacity by offloading macro network traffic. This article reviews the characteristics of cdma2000-based femtocell systems. It discusses design and deployment aspects such as carrier allocation, access control, efficient support for femtocell discovery by idle mobiles, and active call hand-in from macrocell to femtocell. The evolution of the cdma2000 standard for optimizing performance and enriching user experience with femtocells is also discussed.     

Switching plan for a cellular mobile telephone system

Federal Communication Commission Docket 18 262 allocated a 75-MHz band to the common carriers to implement high capacity mobile telephone systems. The Bell System has proposed a cellular arrangement of low-power transmitters/receivers that permits frequency reuse in a coverage area. This method of achieving spectrum efficiency will require extensive centralized coordination and control to properly administer channel assignments and to interconnect the mobiles with each other and with the direct distance dialing (DDD) network. This can be accomplished by means of an electronic switching system (ESS) with special data terminals and trunking arrangements, and a unique program. In the proposed plan the radio sites (base stations) act effectively as remote concentrators in the frequency domain under the control of ESS, which in turn acts primarily as a trunk-to-trunk switcher. In addition to the usual switching, signaling, and supervising functions, the switching office must also perform numerous special functions including paging of mobiles, location of mobiles (signal strength and ranging data analysis), channel reassignment of mobiles, and reswitching of mobiles to various base stations-these last three occurring while customers ate talking.     

Switching Plan for a Cellular Mobile Telephone System

Federal Communication Commission Docket 18 262 allocated a 75-MHz band to the common carriers to implement high capacity mobile telephone systems. The Bell System has proposed a cellular arrangement of low-power transmitters/receivers that permits frequency reuse in a coverage area. This method of achieving spectrum efficiency will require extensive centralized coordination and control to properly administer channel assignments and to interconnect the mobiles with each other and with the direct distance dialing (DDD) network. This can be accomplished by means of an electronic switching system (ESS) with special data terminals and trunking arrangements, and a unique program. In the proposed plan the radio sites (base stations) act effectively as remote concentrators in the frequency domain under the control of ESS, which in turn acts primarily as a trunk-to-trunk switcher. In addition to the usual switching, signaling, and supervising functions, the switching office must also perform numerous special functions including paging of mobiles, location of mobiles (signal strength and ranging data analysis), channel reassignment of mobiles, and reswitching of mobiles to various base stations-these last three occurring while customers are talking.     

Transmit diversity for combined 2G and 3G CDMA systems

In this letter, we propose modifications to existing transmit-diversity techniques to provide transmit diversity in code-division multiple-access cellular systems which must support both second-generation and third-generation mobiles on a common carrier. The proposed method, which we call symmetric-sweep transmit diversity, combines phase-sweep transmit diversity (PSTD) and space-time spreading (STS) in a way that allows second-generation and non-STS-capable mobiles to obtain the full advantage of PSTD, while third-generation mobiles obtain the full advantage of STS.     

Local predictive resource reservation for handoff in multimediawireless IP networks

This paper presents two new methods that use local information alone to predict the resource demands of and determine resource reservation levels for future handoff calls in multimedia wireless IP networks. The proposed methods model the instantaneous resource demand directly. This differs from most existing methods that derive the demands from modeling the factors that impact the demands. As a result, the proposed methods allow new and handoff calls to: (1) follow non-Poisson and/or nonstationary arrival processes; (2) have arbitrary per-call resource demands; and (3) have arbitrarily distributed call and channel holding times. The first method is based on the Wiener prediction theory and the second method is based on time series analysis. Our simulations show that they perform well even for non-Poisson and nonstationary handoff call arrivals, arbitrary per-call bandwidth demands, and nonexponentially distributed call and channel holding times. They generate closely comparable performance with an existing local method and an existing collaborative method that uses information about mobiles in neighboring cells, under assumptions for which these other methods are optimized. The proposed methods are much simpler to implement than most other existing methods with fewer capabilities     

载波聚合技术在卫星移动通信中的适应性初步研究

本文对载波聚合技术在卫星移动通信中的适应性进行了初步讨论,根据不同频段的传输特性,讨论了卫星移动通信载波聚合传输参数的选取方法,给出了一种适合卫星移动通信的载波聚合数据分配方法,通过数值计算和分析,验证了本文所述方法的合理性和有效性。     

E-BAMA vs. RAMA [multiple access protocols]

The article presents a performance comparison of two random access protocols for wireless mobile signaling in which a single channel is dedicated to the signaling function, enhanced beacon assisted multiple access (E-BAMA) and resource auction multiple access (RAMA). Data traffic is transported separately on a set of orthogonal channels. The beacon assisted multiple access (BAMA) protocol was first presented as a method of providing mobility management functions, e.g., handover, while minimizing the processing burden placed on the mobile. In BAMA, throughout the duration of its call, an active user repeatedly and quasi-periodically broadcasts a beacon containing its ID using the Aloha protocol. Quasi-periodicity prevents a pair of users from repeatedly colliding with each other. When a base successfully receives the beacon and assigns a channel, it uses a separate downstream channel to send to the mobile an acknowledgement that contains the number of the assigned channel. The BAMA protocol includes a scheme to maintain lists of active mobiles in nearby cells and to exchange periodically these lists among the base-stations. The authors evaluate the capacity and delay performance of E-BAMA and RAMA. Then, they present a numerical comparison of the parameters. Finally, the results are summarized qualitatively. Some additional derivation is included in the appendix     

Call admission control for an adaptive heterogeneous multimedia mobile network

A novel call admission control (CAC) scheme for an adaptive heterogeneous multimedia mobile network with multiple classes of calls is investigated here. Different classes of calls may have different bandwidth requirement, different request call holding time and different cell residence time. At any time, each cell of the network has the capability to provide service to at least a given number of calls for each class of calls. Upon the arrival (or completion or hand off) of a call, a bandwidth degrade (or upgrade) algorithm is applied. An arriving call to a cell, finding insufficient bandwidth available in this cell, may either be disconnected from the network or push another call out of the cell toward a neighboring cell with enough bandwidth. We first prove that the stationary distribution of the number of calls in the network has a product form and then show how to apply this result in deriving explicit expressions of handoff rates for each class of calls, in obtaining the disconnecting probabilities for each class of new and handoff calls, and in finding the grade of service of this mobile network     

Performance analysis of a cellular network with multiple classes of calls

In this paper, we study a cellular mobile communications network with multiple cells and multiple classes of calls. The different classes of calls have different call holding times and residence time distributions. We consider a protocol mechanism under which a blocked call in a cell is either disconnected from the network or is deemed as a handoff call in a neighboring cell. Under this protocol, we prove that the stationary distribution of this cellular mobile network has a product form. This allows us to derive explicit expressions for handoff rates of each class of calls from one cell to another and the disconnecting probabilities for each class of new and handoff calls. Our numerical results show how these measures depend on the mobility of the mobile terminals in each cell and on the numbers of reserved channels.     

Spectral efficiency and optimal base placement for indoor wirelessnetworks

In this paper, we address the problem of optimizing the spectral efficiency of cellular indoor wireless networks by adjusting the location and power of the base-stations. Focusing on the downlink, we derive general network access criteria for mobiles on the indoor floor for systems that employ omnidirectional antennas and adaptive antennas arrays at the base-stations, in order to show and explain the advantages of the use of spatial diversity. Multiple access capability measures that depend only on energy are defined for both schemes. They are then used as the cost function for the solution to the optimal base-station placement problem, for a single-frequency system. Both continuous and combinatorial approaches have been applied to the solution of the optimization problem, and near-optimal solutions have been obtained. We show that the use of adaptive arrays yields greater capacity when increased cell-area overlap is allowed. The optimization methods, channel prediction methods, and a graphic user interface are parts of an integrated software environment that we developed in support of our investigation and which is described     

Channel reassignment algorithm in multiple carrier hopping TDMAsystems

Channel reassignment schemes used in multiple carrier hopping time-division multiple access (MCH-TDMA) systems are described. In MCH-TDMA systems channels are identified by two degrees of freedom: carrier frequency and time slot. The overlap-chain concept in which related calls from the same transmitting station to the same receiving station are grouped into contiguous streams is introduced. Using this concept, one channel can always be assigned to a call blocked due to inefficient assignment by reassigning channels to calls in progress within two or three time slots. A channel reassignment algorithm called OVERLAP-CHAINING which provides efficient means to reassign channels to calls in progress is proposed     

Study of the effect of excess carrier lifetime depth profiles and depth dependent absorption coefficients on the emitted photoluminescence spectrum of chalcopyrite thin films

The emitted photoluminescence (PL) resulting from radiative recombination in semiconductors is strongly governed by excess carrier density, which is influenced by excess carrier lifetime, absorption coefficient and according boundary conditions at front and rear contact. We have numerically solved the diffusion equation for the excess carrier density with depth dependent lifetime profiles (originating from a depth dependent defect density) and depth dependent absorption coefficient (originating from a depth dependent band‐gap) using a residual control based boundary value problem solver. The emitted PL from the absorber has been calculated on the basis of the excess carrier density with a 1D‐matrix transfer formalism including propagation, multireflection at phase boundaries and reabsorption of PL‐photons. For different lifetime or absorption depth profiles we have characterized the influence on the excess carrier depth profile as well as on the resulting spectral PL yield. Finally the calculated PL spectra were compared to the quasi‐Fermi level splitting from the excess carriers to show the influence of both depth profiles on the shape of the photoluminescence spectrum. Copyright © 2010 John Wiley & Sons, Ltd.     

The Complementary Use of 3G WCDMA and GSM/GPRS Cellular Radio Networks

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.     

Performance of personal portable radio telephone systems with andwithout guard channels

Three call handling schemes for a base station which can handle both originating calls (OCs) and prioritized handoff calls (HCs), and which serves these calls under the blocked-call-delayed basis, are presented and compared. Delayed calls are assumed to be stored in a finite storage buffer. One scheme (Scheme I) exclusively allows handoff calls to be stored and to use a fixed number of guard channels. The other two schemes without guard channels (Scheme II-using the last-in/first-out policy for OC's and Scheme III-using the first-in first-out policy for OC's) allow both types of calls to be stored, and allow prioritized handoff calls to pushout originating calls if the buffer is full. For these three schemes, the blocking probabilities and delay distributions of both types of calls are numerically obtained, and a boundary for call handling schemes between with and without guard channels is found. From the numerical results, it is shown that Scheme II can be considered a good candidate for a call handling scheme for microcellular systems     

Mobility management schemes for real‐time traffic and resource allocation in IEEE 802.16e mobile network

In this paper, our aim is to develop in IEEE802.16e Wireless Networks with link adaptation, in the presence of real‐time traffic call admission control (CAC) schemes. These CAC propose various scenarios of resource splitting and handling the intracell mobility. In particular, we consider two types of intracell mobility classes : low mobility class for mobiles moving usually with low speed between the neighboring regions of the cell and high mobility class for those moving with high speed and that can skip more than one region before changing their modulation. For this reason, we assume a time threshold T _th that determines the minimum time a call must remain in a region before the base station changes its modulation. And we compare it with the time that a call may spend in a region to decide whether the base station will change its modulation or not. In the beginning, we introduce two CAC schemes. In the first one, we reserve a portion of resources to mobiles in migration with both high and low mobility. And in the second one, we give the priority just to mobiles in migration with high mobility. Then, we calculate the impact in the blocking and dropping probabilities. We show by numerical results that by the proposed CAC schemes, we can find a resource management that outperforms well under different types of mobility. But, to find a good tradeoff between dropping the calls in migration and blocking the new calls, we introduce the optimization problem in the second part. So, we are faced to the necessity of optimizing the results found in the first part. Therefore, we define an objective function to optimize, in order to ensure the highest quality of service for users and to give a better stability state between the dropping and blocking probability. We show that the proposed objective function gives the optimal resources allocation between the migrating and new arriving calls in the cell. Copyright © 2015 John Wiley & Sons, Ltd.     

Adaptive quality of service handoff priority scheme for mobilemultimedia networks

For various advantages including better utilization of radio spectrum (through frequency reuse), lower mobile transmit power requirements, and smaller and cheaper base station equipment, future wireless mobile multimedia networks are likely to adopt micro/picocellular architectures. A consequence of using small cell sizes is the increased rate of call handoffs as mobiles move between cells during the holding times of calls. In a network supporting multimedia services, the increased rate of call handoffs not only increases the signaling load on the network, but makes it very difficult for the network to guarantee the quality of service (QoS) promised to a call at setup or admission time. This paper describes an adaptive QoS handoff priority scheme which reduces the probability of call handoff failures in a mobile multimedia network with a micro/picocellular architecture. The scheme exploits the ability of most multimedia traffic types to adapt and trade off QoS with changes in the amount of bandwidth used. In this way, calls can trade QoS received for fewer handoff failures. The call level and packet level performance of the handoff scheme are studied analytically for a homogeneous network supporting a mix of wide-band and narrow-band calls. Comparisons are made to the performance of the nonpriority handoff scheme and the well-known guard-channel handoff scheme     

Channel reservation for handoff calls in a PCS network

Some new performance measures and channel reservation for handoff calls for maximizing the service provider's revenue in a personal communications service (PCS) network, with general cell residence time and general requested call holding time, are investigated. Here, each cell within the PCS network consists M channels, but only when at least m+1 (0⩽m<μ) channels are available will a new originating call be accepted. A handoff attempt is unsuccessful if no channel in the target cell is available. Some new performance measures of the system such as the modified offered load (MOL) approximations of the blocking probability of new and handoff calls, the distribution and the mean actual call holding time of a new call and related conditional distributions and the expectations, as well as the boundary of the mean of the actual call holding time of an incomplete call and a complete call are obtained. A necessary and sufficient condition for maximizing the provider's revenue is achieved for any general cost structure if it is an increasing function of the actual call holding time. In order to be fair to the customers with incomplete call and complete call, two different kinds of holding costs are considered for the different customers. In both situations, the optimal controlling value m of handoff priority is obtained by maximizing the service provider's revenue     

Variable-band hysteresis current controllers for PWM voltage-sourceinverters

Hysteresis current controllers having fixed bands are used in inverters of high-performance AC drives. The switching frequency of such controllers varies over the fundamental period of the modulating signal. The maximum switching frequency (MSF) of these controllers is high. To limit the MSF within the limit of inverter switches, fixed carrier lockouts are usually incorporated. The incorporation of carrier lockouts causes current distortion, and load currents do not confine within the predetermined band. In this paper, two new controllers are proposed. One is a mixed-mode controller of sinusoidal band added to a fixed band, and the other is an equidistant-band current controller, performances of the proposed controllers are compared with the performances of the conventional fixed-band and sinusoidal-band controllers     

Modeling and analysis of hierarchical cellular networks with general distributions of call and cell residence times

We present an analytic model for the performance evaluation of hierarchical cellular systems, which can provide multiple routes for calls through overflow from one cell layer to another. Our model allows the case where both the call time and the cell residence time are generally distributed. Based on the characterization of the call time by a hyper-Erlang distribution, the Laplace transform of channel occupancy time distribution for each call type (new call, handoff call, and overflow call) is derived as a function of the Laplace transform of cell residence time. In particular, overflow calls are modeled by using a renewal process. Performance measures are derived based on the product form solution of a loss system with capacity limitation. Numerical results show that the distribution type of call time and/or cell residence time has influence on the performance measure and that the exponential case may underestimate the system performance.