Alagan S. Anpalagan

Overlaid cellular system design with cell selection criteria for mobile wireless users

As the cells shrink and mobility increases in personal communication services (PCS), an increased number of handoff occurs overloading the signaling network. One major motivation to employ microcell/macrocell overlays is to increase the capacity without increasing the handoff rates. A cellular system consisting of two tiers with microcell in the lower-tier and multiple levels of (macro)cells in the upper-tier, is considered to separately serve mobiles with different speeds. The dimension of the upper-tier cell is approximately derived based on the mean velocity of mobiles the cell intends to serve. Finally, the effect of misusing the upper-tier resources is analyzed in terms of each tier call blocking rate.

A combined rate/power/cell control scheme for delay insensitive applications in CDMA systems

A novel combined rate, power and cell (R/P/C) control scheme that gracefully implements congestion control, is proposed and studied. We consider the reverse link in a CDMA network with a high degree of traffic fluctuations spatially with time, as would be the case in future wireless systems. Our scheme attempts to reduce the high interference power variations among cell-site antennas that can exist in a real network. The transmission rates of those users in the congested (non-congested) cells are decreased (increased) providing the required average throughput among users; hence, the proposed scheme is appropriate for delay insensitive applications. We consider the minimization of the average transmit bit energy (/spl Theta/) subject to maintaining individual target E/sub b//I/sub 0/ for each user. Two algorithms, one directly minimizing /spl Theta/ and the other indirectly using measured pilot power, are given. Both algorithms select the optimal cell-site if forward and reverse link gains are equal; however, the latter is decentralized and uses only local measurements and amenable for practical implementation. Simulation results show that a 20% reduction in transmit bit energy can be achieved on average using our schemes over the scheme with no rate control.

On the receive power allocation in a cellular multimedia CDMA system with fixed base station assignment

In this paper, we consider the receive power allocation (RPA) problem for multimedia users in a cellular CDMA network. It is shown that the problem can be split into two optimization problems, source-based RPA (SBRPA) and network-based RPA (NBRPA). SBRPA determines the relative receive power levels (RPLs) between different classes of users in each cell irrespective of the intercell interference and it is locally implemented. NBRPA determines the relative RPLs between cells and can be achieved solving an eigenvalue problem with the system-wide class-wise SIR-balancing and it is globally implemented. The need for interference-balancing to increase the capacity with minimum mobile transmit power is emphasized. Finally, numerical results are presented to demonstrate the effectiveness of the proper RPA in a cellular multimedia CDMA system.

Adaptive cell sectoring using fixed overlapping sectors in CDMA networks

The problem of base station antenna assignment (BSAA) with minimum mobile transmit power (MTP) is studied for CDMA networks that employ fixed overlapping sector antenna architecture (FOSAA). It is noted that the non-FOSAA has limitations in switching users between in-cell sectors and also out-of-cell sectors in moderately loaded networks. It is then shown that by employing overlapping sectors in FOSAA, we can exploit the flexibility of assigning a user to one of possibly many potential antenna to effectively support the non-uniform angular traffic. It is also proven that the problem of selecting a set of antenna from a pool of overlapping antenna and assigning the users to them in FOSAA with minimum MTP is a special case of a general problem that was solved by Hanly (1995) and Yates (1995). The process of dynamic cell sectoring is differentiated two-fold as cell-breathing (CB) and cell-slicing (CS) and the latter can be viewed as azimuthal counterpart of the former radial scheme. The hybrid scheme, CB+CS, is shown to yield the optimal solution in minimum total MTP in a CDMA/FOSAA system. The performance results for the total MTP and the received signal quality are reported. As the congestion level increases, the difference in SIR performance between CB and CS schemes becomes more apparent with the latter outperforming the former. The performance results also show that on average, the CB scheme requires about 30% more power than in CB+CS, when 60% of the mobiles are concentrated in a hot-spot sector in a conventional 3-sector cell.

A tagging-based medium access scheme for wireless data applications in CDMA/TDM networks

In this paper, a packet scheduling scheme based on real-time channel conditions and avoidance of dominant inter-cell interferers is proposed and studied. This scheme is implemented by the distribution of tags by receivers among transmitters. We focus on reverse links of a CDMA/TDM system where for every slot, each base station issues M(/spl ges/1) tags to M mobile users (MU) based on the ranked reverse link gains. The number of tags thus issued depends on the expected traffic, the number of cells and the propagation conditions in the network. Two types of tags can be issued: eg, hard and soft tags. A MU will transmit only if it receives a tag from its home base station (BS) and no hard tag from any other BS. Hence, in our scheme, MU that not only have stronger channel pins to their respective home BS but also cause relatively lower inter-cell interference are scheduled for transmissions. This scheme is hence a cooperative approach whereby good-neighbor behaviour is exhibited. Soft-tagging offers flexibility in allowing MU that cause moderate inter-cell interference to transmit under certain conditions such as longer starved time. Simulation results in shadow and a Rayleigh failing environment are presented to show that our scheme outperforms the conventional scheme by 30% in transmit bit energy when M = 10 in a 9-cell network with 100 MU uniformly distributed.

Reverse link performance analysis of a cellular CDMA network with fixed overlapping sectors in non-uniform angular traffic

We study the reverse link performance of a cellular CDMA network that employs fixed overlapping sector antenna architecture (FOSAA) in a hot-spot environment. Simulation results demonstrate the flexibility and effectiveness of the FOSAA in non-uniform angular traffic. The CDF statistics of received SIR are presented for different congestion levels in hot-spot sectors. A scheme with FOSAA can yield on the average 0.8 dB SIR increase over a scheme without FOSAA, when 60% of the mobiles is concentrated in a hot-spot sector in a conventional 3-sector cell. The performance measures such as the mobile transmit power and the antenna selection and sector coverage are also studied.

A Distributed Packet Scheduling Scheme with Interference Avoidance for Non Real-Time Applications in CDMA Networks

In this paper, a packet scheduling scheme based on real-time channel conditions and dominant intercell interferer avoidance is proposed, studied and evaluated for reverse links in a time-slotted code division multiple access (CDMA) system. This scheme is implemented by distribution of tags by receivers among transmitters. Each base station issues M(≥1) tags to M mobile users based on the ranked reverse link gains in every slot. M=1 corresponds to spread-spectrum time division multiplexing mode operation and M≥1 corresponds to scheduling multiple simultaneous transmissions as in the traditional CDMA systems. The number of issued tags is a system parameter which depends on the expected traffic, the number of cells and the propagation conditions in the network. In the proposed scheme, users who not only have stronger channel gains to their respective home base stations but also cause relatively lower intercell interference are scheduled for transmissions. Different classes of tags can be issued and various scheduling decision rules can be implemented giving flexibility in interference management. Simulation results in shadow and multipath fading environment are presented to show the performance advantage of the proposed scheme.

On the integrated transmit power control and base station assignment in reverse links of cellular CDMA networks

CDMA systems are inherently interference limited and dynamic power control combined with dynamic base station assignment has been effective in reducing the transmitter power and hence increasing the system capacity. The paper discusses the performance of a load balanced network that is implemented using an integrated, dynamic transmit power control and base station assignment scheme. Simulation results showing the effect of dynamic load sharing and balancing are also presented.

A study of DiffServ based QoS issues in next generation mobile networks

To provide data rates of the order of hundreds of Mbps and multimedia services, standardization efforts for next generation (4G) systems are focusing on target technologies and seamless connectivity through various types of networks, including wireline networks and WLANs. Different types of multiple access techniques, such as the ones based on multicarrier CDMA and OFDM (orthogonal frequency division multiplexing) have been proposed. There is a need for functional integration of the multiple networks, and, with the evolution of IPv6 and QoS support for IP networks, an IP based interconnectivity is best suited. A QoS aware adaptive radio resource management technique based on multi-code multicarrier CDMA is discussed. We develop a novel radio access method and develop algorithms for allocating and controlling radio network resources so that system performance can be maximized and guaranteed QoS for multimedia services can be provided within the DiffServ environment.

Integrated rate, power and cell control in cellular CDMA systems: an interference-balancing approach

In this paper, a novel combined rate, power and cell control scheme that minimizes transmit bit energy while gracefully implementing the congestion control is proposed and studied. The reverse link in a code division multiple access (CDMA) system with a high degree of traffic fluctuation temporally as well as spatially is considered. The proposed radio resource management scheme attempts to reduce the interference power variation among base station antennas that can exist in a real radio network. Transmission rates of those users in the congested (non-congested) cells are decreased (increased); hence, the proposed scheme is appropriate for delay-insensitive variable-bit-rate applications. Minimization of average transmit bit energy is achieved, subject to maintenance of individual target Eb/I0 for each user. Two algorithms, one directly minimizing the transmit bit energy, and the other doing so indirectly using the measured pilot power, are presented. It can be shown that both algorithms select the optimal base station if forward- and reverse-link gains are reciprocal; however, the latter gain is decentralized and uses only the local measurements and is amenable for practical implementation.