Erlang Capacity of a Voice/Data Cellular CDMA Uplink System Using Prioritized Admission Control and Adaptive Power Control

A CDMA uplink system that carries both voice and data traffic is investigated. The reservation-based admission control scheme is used to prioritize voice mobiles, and the truncated channel inversion power control scheme is used by data mobiles to improve system capacity. The performance of the system is measured by the Erlang capacity. Two methods of determining the Erlang capacity are presented. The first method decouples the analysis of blocking and outage performance, thus simplifying numerical search. The second method takes into account the impact of mobile traffic fluctuations on interference statistics, and thus yields more accurate results. Numerical results are provided that show significant differences between the two methods. Finally, the Erlang capacities of the system are compared for different power control schemes.     

Improved Erlang capacity of combined carrier channel assignment for hybrid FDMA/CDMA systems supporting voice and data services

Using analytical techniques, we determine the conditions under which the combined carrier channel assignment (CCCA) scheme of channel allocation is preferable to the independent carrier channel assignment (ICCA) in an FDMA/CDMA system providing voice and circuit-switched data services. We find out that, even though the benefit of the CCCA scheme over the ICCA scheme is negligible for small number of channel elements (CEs), the scenario changes significantly when the number of CEs increases beyond a certain point. An improvement of as much as 74% can be achieved in the Erlang capacity when 5 carriers are employed, each with 29 channels in a 3-sector per cell system. We also find the capacity knees for different number of carriers.     

一种CDMA系统反向功率控制的算法

本文简要介绍了基于ＩＳ－９５的ＣＤＭＡ系统反向信道功率控制的原理及其算法实现，从理论上分析了理想的精确功率控制和非精确功率控制对反向信道爱尔兰容量的影响，并对反向闭环功控算法和外环功率控制算法进行了仿真，得到爱尔兰容量最大的仿真算法。     

Performance evaluation of a reservation random access scheme for packetized wireless systems with call control and hand-off loading

We consider a packet switched wireless network where each cell's communication channel is shared among packet voice sources. In this paper, we present a method for the design and analysis of wireless cells using a reservation random access (RRA) scheme for packet access control. This scheme is integrated with a call admission control procedure. We model the state process of a single cell as a vector Markov chain. We compute the steady state distribution of the Markov chain. This result is used to calculate the packet dropping probability and the call blocking probability. By setting limits on maximum permissible levels for the call blocking probability and the packet dropping probability, we obtain the Erlang capacity of a single cell, with and without hand-off traffic. For an illustrative RRA scheme, the Erlang capacity of a single cell is shown to be about twice that attained by a comparable fixed assigned TDMA scheme. We show that a cellular network using this RRA scheme and which applies can be no blocking of hand-off calls, exhibits similar call capacity levels.This work is supported by a University of California MICRO and Pacific-Bell Grant No. 94-107.     

Erlang capacity of a power controlled CDMA system

This work presents an approach to the evaluation of the reverse link capacity of a code-division multiple access (CDMA) cellular voice system which employs power control and a variable rate vocoder based on voice activity. It is shown that the Erlang capacity of CDMA is many times that of conventional analog systems and several times that of other digital multiple access systems     

功率控制对S-CDMA-HFC系统上行信道Erlang容量的影响

同步ＣＤＭＡ（Ｓ－ＣＤＭＡ）解决了双向ＨＦＣ系统的上行信道噪声和容量问题,基于Ｓ－ＣＤＭＡ的ＨＦＣ是新一代ＨＦＣ系统。从系统实现的角度来看,非理想功率控制会明显降低系统业务容量。本文简单介绍了Ｓ－ＣＤＭＡ－ＨＦＣ系统模型和上行信道概况,分析了非理想功率控制对Ｓ－ＣＤＭＡ－ＨＦＣ系统上行信道Ｅｒｌａｎｇ容量的影响,并给出了数值结果与结论。     

Reverse-link capacity of power-controlled CDMA systems with beamforming

In this paper, reverse-link capacity, in terms of user capacity and Erlang capacity, of a direct-sequence code-division multiple-access (DS-CDMA) system with the use of beamforming is investigated. Signal-to-interference ratio (SIR)-based power control is assumed and both transmit and receive beamforming are considered. Instead of using tedious iterative methods to evaluate user capacity, a simple closed-form capacity expression with respect to antenna gains, a target SIR, and the CDMA processing gain is derived. Numerical results indicate significant capacity improvement with beamforming. The impact of the estimation errors of arrival angles on the capacity is examined. The joint use of a RAKE receiver and beamforming is investigated and the capacity expression for CDMA systems with multiclass services is also derived.     

Erlang capacity of multiaccess systems with service-based access selection

In this letter, we provide the lower and upper bounds of Erlang capacity of multiaccess systems supporting several different radio access technologies in the multiservice scenario, by considering two extreme operation methods; separate and common operation. In a numerical example with GSM/EDGE-like and WCDMA-like subsystems, it is shown that the common operation method can provide up to 60% Erlang capacity improvement over the separate operation method when using a near optimum so-called service-based user assignment scheme, with the combined effects of the assignment and the trunking gains. Even in the worst-case, the common operation method still can provide about 15% capacity improvement over the separate operation method, which mainly comes from the trunking gain.     

Spectrally efficient modulation and spreading scheme for CDMAsystems

A novel modulation and spreading scheme is proposed based on the orthogonal complex rotator that outperforms the traditional PN (pseudo noise) complex QPSK method in terms of adjacent channel power. This scheme is important for hand-held terminals because it increases battery life and capacity due to reduced interference. A mathematical analysis and adjacent channel power simulation results are provided and discussed     

Resource allocation for cellular radio systems

High terminal traffic densities are expected in urban multiuser radio systems. An efficient allocation of resources is the key to high system capacity. In this paper, a distributed dynamic resource allocation (DDRA) scheme based on local signal and interference measurements is proposed for multiuser radio networks. It offers “soft capacity” for time division multiple access (TDMA) and frequency division multiple access (FDMA) systems, bounded above by N per base station, where N is the total number of channels in the system. The decisions are made local to a terminal and its base and are essentially independent of the rest of the system. A distributed dynamic channel assignment scheme is used to assign channels to new calls. This scheme assigns a channel that offers the maximum carrier to interference ratio (CIR) to a new call. A distributed constrained power control (DCPC) scheme based on CIR measurements is used for power control. The channel assignment scheme and the power control scheme are coupled to obtain an interactive resource allocation scheme. We compare the capacity of a system which uses the distributed dynamic resource allocation scheme described above with the capacity of a system which uses the channel assignment scheme alone. The system capacity is measured by simulation as the number of terminals that can be served by the system with a CIR above an acceptable minimum. In a 1D cellular system, coupling the channel assignment scheme with power control is discussed. Simulations were also used to show the effect of varying the maximum transmitter power on system capacity     

Full- and half-square cell plans in urban CDMA microcellular networks

The Erlang capacity per cell and per unit area in urban code-division multiple-access (CDMA) microcellular environments is evaluated. Special emphasis is given to the effect of breakpoint distance and cell size on the system Erlang capacity. Two different cell plans are considered in which the communication between the base station (BS) and the mobile unit always occurs in a line-of-sight (LOS) condition: the full- and half-square cell plans. Our main result has been to obtain analytical expressions for the Erlang capacity, which are evaluated through a cell radius-normalization procedure, as a function of the breakpoint to the cell radius ratio (R/sub b//R/sub c/). This has allowed us to notice some important facts not previously reported in the literature. In particular, we observe that the Erlang capacity is a monotonically decreasing function of R/sub b//R/sub c/ and that close to the highest reuse efficiency is achieved for R/sub b/<0.7R/sub c/. Thus, given a breakpoint distance, higher Erlang capacity per cell can be achieved with greater cell radius. Or, equivalently, given a cell radius, higher system capacity can be achieved with smaller breakpoint distances; that is, with smaller base-station antenna heights and/or smaller frequencies. Also, we show that the capacity increase due to the BSs doubling or cell radius-reduction depends on the antenna heights, frequency of operation, and distance between streets. It ranges from 64 to 100%.     

Interference coordination schemes for cellular network assisted device-to-device multicast

In this paper, a multicast concept for device-to-device （D2D） communication underlaying a cellular infrastruc~tre is investigated. To increase the overall capacity and improve resource utilization, a novel interference coordination scheme is proposed. The proposed scheme includes two steps. First, in order to mitigate the interference from D2D multicast transmission to cellular networks （CNs）, a dynamic power control scheme is proposed that can determine the upper bound of D2D transmitter power based on the location of base station （BS） and areas of adjacent cells from the coverage area of D2D multicast group. Next, an interference limited area control scheme that reduces the interference from CNs to each D2D multicast receiver is proposed. The proposed scheme does not allow the coexistence of cellular user equipments （CUEs） located in the interference limited area to reuse the same resources as the D2D multicast group. From the simulation results, it is confirmed that the proposed schemes improve the performance of the hybrid system compared to the conventional ways.     

Computing approximate blocking probabilities for large lossnetworks with state-dependent routing

A reduced load approximation (also referred to as an Erlang fixed point approximation) for estimating point-to-point blocking probabilities in loss networks (e.g., circuit switched networks) with state-dependent routing is considered. In this approximation scheme, the idle capacity distribution for each link in the network is approximated, assuming that these distributions are independent from link to link. This leads to a set of nonlinear fixed-point equations which can be solved by repeated substitutions. The accuracy and the computational requirements of the approximation procedure for a particular routing scheme, namely least loaded routing, is examined. Numerical results for six-node and 36-node asymmetric networks are given. A novel reduced load approximation for multirate networks with state-dependent routing is also presented     

Forward-link capacity of a DS/CDMA system with mixed multiratesources

Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems     

CBWL: a new channel assignment and sharing method for cellularcommunication systems

A new scheme that allows cell gateways (base stations) to borrow channels from adjacent gateways in a cellular communication system is presented. Borrowed channels are used with reduced transmitted power to limit interference with cochannel cells. No channel locking is needed. The scheme, which can be used with various multiple access techniques, permits simple channel control management without requiring global information about channel usage throughout the system. It provides enhanced traffic performance in homogeneous environments and also can be used to relieve spatially localized traffic overloads (tele-traffic `hot spots'). Co-channel interference analysis shows that the scheme can maintain the same SIR as nonborrowing schemes. Analytical models using multidimensional birth-death processes and decomposition methods are devised to characterize performance. The results which are also validated by simulation indicate that significantly increased traffic capacity can be achieved in comparison with nonborrowing schemes     

Terminal density dependent resource management in cognitive heterogeneous networks

In cognitive heterogeneous network, when multitudes of femtocells coexist, effective resource management become important to enhance network performance. Based on the base station location and terminal distribution density, we propose spectrum management and power configuration scheme for femtocells deployment network. In the beginning, we consider two femtocells adjacent network and propose the resource management scheme. The scheme allocates time frequency resource by adopting complete reusing and private usage in non-overlapping and overlapping areas respectively. Subsequently the scheme optimizes base station power under the constraints of cross-tier interference and maximal transmission power to maximize network capacity. According to the analysis of the power variation effect to femtocell coverage, a near-optimal solution of the transmission power is derived, and the corresponding power configuration scheme is proposed. After then we extend the spectrum and power management to multiple femtocells coexisting networks, and propose the management scheme applied for multiple femtocells deployment networks. The simulation results indicate that in capacity performance, the proposed power solution is close to the optimal solution, and the proposed resource management outperforms the existing schemes.     

An inter-lighting interference cancellation scheme for MISO-VLC systems

In this paper, we propose an inter-lighting interference cancellation (ILIC) scheme to reduce the interference between adjacent light-emitting diodes (LEDs) and enhance the transmission capacity of multiple-input–single-output (MISO)-visible light communication (VLC) systems. In indoor environments, multiple LEDs have normally been used as lighting sources, allowing the design of MISO-VLC systems. To enhance the transmission capacity, different data should be simultaneously transmitted from each LED; however, that can lead to interference between adjacent LEDs. In that case, relatively low-received power signals are subjected to large interference because wireless optical systems generally use intensity modulation and direct detection. Thus, only the signal with the highest received power can be detected, while the other received signals cannot be detected. To solve this problem, we propose the ILIC scheme for MISO-VLC systems. The proposed scheme preferentially detects the highest received power signal, and this signal is referred as interference signal by an interference component generator. Then, relatively low-received power signal can be detected by cancelling the interference signal from the total received signals. Therefore, the performance of the proposed scheme can improve the total average bit error rate and throughput of a MISO-VLC system.     

Effective Interference Cancellation Schemes for Device-to-Device Multicast Uplink Period Underlaying Cellular Networks

Device-to-Device (D2D) multicast will become an important technology with the increasing requirements of local communication services in future networks. To increase the overall capacity and improve resource utilization, a novel interference coordination scheme is proposed. The proposed scheme includes three steps. First, in order to mitigate the interference from D2D multicast transmission to cellular networks (CNs), a dynamic power control scheme is proposed that can determine the upper bound of D2D transmitter power based on the location of Base Station and areas of adjacent cells from the coverage area of D2D multicast group. Next, an interference limited area control scheme that reduces the interference from CNs to each D2D multicast receiver is proposed. The proposed scheme does not allow the coexistence of cellular equipments (CUEs) located in the interference limited area to reuse the same resources as the D2D multicast group. Then two resource block (RB) allocation rules are proposed to select the appropriate RBs from a candidate RB set for D2D multicast group. From the simulation results, it is confirmed that the proposed schemes improve the performance of the hybrid system compared to the conventional ways.     

A parametric power control with fast convergence in cellular radiosystems

The capacity of a cellular radio system is largely dependent on its transmitter power control. Since power control is inherently a real-time problem, to find the fastest carrier-to-interference ratio (CIR) balancing algorithm, which forces the CIR of each cell to converge to a value, has been the essential issue. An efficient parametric power control (PPC) scheme is developed in this paper. In this scheme, the power control is performed at each base by using some parameters provided by the central collector, which determines the multiplier of the power update function. The algebraic property of its CIR balancing algorithm is analyzed. In an environment with zero noise, the scheme proposes a quick method for obtaining a least upper bound on the achievable CIR. The proposed scheme PPC is also considered in a cellular system with positive receiver noise. The computational results show that the convergence of the proposed CIR balancing algorithm is quick and the power consumption is reasonable compared to distributed schemes. With the proposed algorithm, the CIR's are balanced sufficiently in a short power control period     

Uplink capacity optimization by power allocation for multimedia CDMA networks with imperfect power control

A closed-form capacity quasi-optimal power allocation scheme is presented for the uplink of multimedia code-division multiple-access (CDMA) systems with randomized received signal-to-interference ratio (SIR) resulted from the errors of power control. The optimality in capacity comes from that this scheme provides class-dependent SIR margins subject to the constraint of differentiated outage requirements. The statistics of signal under imperfect power control is modeled as lognormal random variable. The objective of capacity maximization is formulated as the minimization of total average received powers since the capacity of a CDMA system is interference limited. Under this model, we first derive the necessary conditions that a capacity-optimal power allocation should satisfy. By using conservative bounds, we provide a closed-form approximate solution to this optimization problem. This approximate solution provides nearly the same admissible region for multimedia traffic under imperfect power control as the accurate solution (the optimal one) does. The closed-form quasi-optimal power allocation scheme proposed in this paper is just based on this approximate solution. By numerical example we verify our analysis and show that great capacity gain (e.g., 92% as a maximum in the example) can be achieved by our scheme over its counterpart.