Jeongrok Yang

Capacity-optimized power allocation scheme in an integrated voice and data DS-CDMA system

In this paper, a power allocation scheme is proposed to enhance the system capacity, defined as the sum of throughput for data users and Erlang capacity for voice users in a mixed voice and data DS-CDMA system. The proposed scheme increases the supportable data traffic load which is limited to satisfy the pre-determined QoSs of voice users such as the required BER, by allocating the transmission power of the data users to be less than that of voice users. Through a numerical example, this scheme shows the enhancement of system capacity. Especially, we can get double system capacity by allocating the transmission power of data users to be half of that of voice users, given the voice traffic load of 0.1.

Erlang capacity analysis of hybrid FDMA/CDMA systems supporting multi‐class services according to channel assignment methods

In this paper, we focus on the evaluation of the Erlang capacity for hybrid FDMA/CDMA systems supporting multi-class services with two channel allocation schemes: independent carrier channel assignment (ICCA) and combined carrier channel assignment (CCCA). For the performance analysis, a multi-dimensional Markov chain model is developed. The effect of the number of carriers of hybrid FDMA/CDMA system on the Erlang capacity is observed, and the optimum values of the system parameters such as the number of channel elements (CEs) and the number of carriers are selected with respect to the Erlang capacity. As a numerical example, we consider an FDMA/CDMA system supporting voice/data services. We find out that, even though the benefit of CCCA scheme over ICCA scheme is negligible for small number of 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. We also find the capacity knees for different number of carriers. The results of this paper could be helpful in the traffic engineering of FDMA/CDMA systems providing multi-class services. Copyright

An approximate analysis method of Erlang capacity for CDMA systems with multiple sectors, and multiple frequency allocation bands

It is a practical problem for traffic engineers to determine the proper number of channel elements (CEs) in the base station that are required to support given offered traffic loads. Kim (see Handbook of CDMA System Design Engineering and Optimization, Prentice Hall, 1999) properly deals with this problem, however, the analytic method proposed in the reference requires tedious calculation for computing call blocking probability, especially when the system supports multiple sectors and multiple frequency allocation bands. We propose an approximate analysis method reducing the exponential complexity of the old method down to the linear complexity. Further, the approximated results provide only a few percent difference from the exact value, which is practically useful.

Analysis of Erlang capacity for DS-CDMA systems supporting multi-class services with the limited number of channel elements

In practice, the DS-CDMA system is equipped with a finite number of channel elements (CEs) that performs the baseband spread signal processing for a given channel in the base station. In this situation, the call blocking can be caused not only by the insufficient number of channel elements but also by the limit of available traffic channels. We focus on analyzing the effect of the limited number of CEs on the Erlang capacity of multimedia DS-CDMA systems in the reverse link when the CDMA cells are sectorized with 3 sectors. For the performance analysis, a multi-dimensional Markov chain model is developed. As a result, the more CE results in the larger Erlang capacity. However, the Erlang capacity is saturated after a certain value of CEs where the call blocking is mainly caused by the insufficient channels per sector.

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.

A dynamic resource allocation scheme to maximize throughput in a multimedia CDMA system

In this paper, a resource allocation scheme is proposed to maximize the throughput of a multimedia CDMA system. When we let the throughput be a function of various data rates for multimedia traffic, the scheme is to find the optimum set of data rates for concurrent user groups which makes the system throughput maximize. It is shown that the optimum data rate set includes one non-trivial rate while all others keep the minimum required data rate, where the non-trivial rate is assigned dynamically to one group out of the set of VBR groups according to various QoS requirements and the number of users.

Flexible call admission control schemes for DS-CDMA systems with non-uniform traffics

In a DS-CDMA system, due to the inter-cell interference, the resources of a cell are occupied not only by the users in the home cell but also by the users in neighboring cells. When the traffic load is high in a DS-CDMA system, allowing a local user to occupy resources sometimes blocks several call requests in the neighboring cells. In this paper, flexible CAC schemes are proposed as a solution to the above problem and compared with conventional CAC scheme under uniform and non-uniform traffic distributions. Flexible CAC schemes reserve small part of resources for call requests in other cells instead of accepting a call request in its own cell. Reserving small part reduces the overall average blocking rate when the traffic load is high. Especially when the traffics are non-uniform. A flexible CAC scheme outperforms a conventional CAC scheme.

Delay Distribution of Data Calls in Integrated Voice/Data CDMA Systems

In this letter, we present a procedure to analyze the delay distribution of data traffic in CDMA systems supporting voice and delay-tolerant data services with a finite buffer. The queueing method using a buffer for a delay-tolerant traffic can be used to improve the system utilization or the availability of system resources. Under the first-come and first-serve (FCFS) service discipline, we present a numerical procedure for the formation of delay distribution that is defined as the probability that a new data call get a service within the maximum tolerable delay requirement, based on a two-dimensional Markov model.

Erlang capacity of voice/data CDMA systems with service requirements of blocking probability and delay constraint

In this paper, we investigate the Erlang capacity of a CDMA system supporting voice and data services with service requirements of blocking probability and delay. We define the delay confidence defined as the probability that a new data call is accepted within the maximum tolerable delay without being blocked. In this case, the Erlang capacity is confined not only by the required blocking probability of voice call but also by the required delay confidence of data call. For the performance analysis, we develop a two-dimensional Markov model, and we derive the CDF of delay and subsequent relation for the delay requirement. Further we present a numerical procedure to analyze the Erlang capacity under a given blocking probability and delay confidence. As a result, it is necessary to make a balance between the Erlang capacity with respect to the blocking probability of voice call and that with respect to the delay confidence of data call so as to accommodate the more Erlang capacity.