Diego Antonio Lara Rodriguez

• Cooperative University of Colombia

Traditional scheduling algorithms are focused in maximizing system throughput considering a grade of fairness. However, maximizing the system throughput does not necessarily result in maximizing the number of satisfied users (users with a packet delay below a threshold). Also, the throughput maximization could cause a low grade of fairness. In this...

Traditional scheduling algorithms are focused in maximizing system throughput considering a grade of fairness. However, maximizing the system throughput does not necessarily result in maximizing the number of satisfied users (users with a packet delay below a threshold). More over, the throughput maximization could cause a low grade of fairness. In...

Smart antennas have received increasing interest due to its capability for improving the performance of wireless radio systems. In this work we studied the throughput maximization in a CDMA 1xEV-DO cellular system when a smart antenna array is implemented. We focus in the downlink of the CDMA cellular system and consider a packet data direct-sequen...

The CDMA overlay concept, has been proposed as one alternative to take advantage of the bandwidth available in narrowband systems. In fact, the basic idea of the CDMA overlay is to allow to wideband CDMA wave forms, to share a common spectrum with narrowband conventional wave forms. In this work, we have focused in the analysis of the performance o...

In this paper, a novel prioritization mechanism for random access strategies in cellular networks is proposed. The proposed prioritized random access strategy sets different retransmission probabilities to users, depending on their priorities. First, a mathematical analysis method for simultaneously evaluating throughput and access delay, consideri...

Propagation loss is a fundamental phenomenon that affects the performance of any wireless network. Although propagation characteristics in line-of-sight (LOS) microcellular systems are well known, so far, only a few papers have investigated its effect on system performance in a comprehensive manner. In this paper, the impact of both system paramete...

In this paper, we evaluate the maximum uplink user capacity of a Macrocell/Microcell Cellular CDMA System under non-uniform traffic loading conditions. The "hot spots" microcells are embedded within a large macrocell and operate over the same bandwidth as the large cell. The analytic method to compute Erlang user capacity takes into accounts propag...

In this paper we evaluate the uplink user capacity of a macrocell/microcell CDMA system under non-uniform traffic loading conditions. The "hot spots" microcells are embedded within a large macrocell and operate over the same bandwidth as the large cell. The analytic method to compute Erlang user capacity takes into account propagation and shadowing...

Wireless communication has emerged as the most promising and one of the leading sectors of the telecommunications industry in the 21st century. To appreciate the expansion of the wireless sector, in 1990, there were only ten million cellular phone subscribers worldwide that frequently use first-generation technology. Today, there are more than one...

In this work, we evaluate the performance of a CDMA cellular system with integrated services: voice and data. The activity of voice user is an exponential ON/OFF model. The data user session is a WWW browsing type. When a base station transmits information to a user it does it through supplemental code aggregation. We evaluated the impact of data u...

In this paper, the throughput maximization and fairness problems in the downlink of a sectorized CDMA cellular system are studied. We focus in maximizing the data rate for users on the cell border. An optimum data transmission with power control allocates the maximum allowable rate to only one user with the highest SINR. However, this throughput ma...

In this paper, the mobility/capacity conversion (MCC) efficiency of reuse-based resource management strategies in multi-service wireless communication networks is mathematically analyzed. In particular, a useful and efficient resource management strategy is proposed and evaluated. The proposed strategy exploits the synergy between the maximum packi...

In this paper, a mathematical analysis method to simultaneously evaluate throughput and access delay considering an infinite population model is considered. Most of the previous related research has been done considering both finite population and saturation conditions where all the nodes in the system have always a packet ready to be transmitted a...

In this paper, the throughput maximization and fairness problems in the downlink of a sectored CDMA cellular system with AMC techniques are studied. We focus on maximizing the data rate for users on the cell border. An optimum data transmission with power control allocates the maximum allowable rate to only one user with the highest SINR. However,...

In this letter, closed-form non-recursive expressions for the probability mass function (pmf) of the access delay are addressed. As the exact non-recursive expression for the pmf of the access delay are typically complex and have high computational requirements, Gaussian approximations are derived for the uniform, binary exponential and geometric b...

The performance of the forward link supporting data services in microcellular system based on the cdma2000 standard is evaluated, using a mix of static and dynamic simulation approaches. We consider the ideal Manhattan-like street pattern, so two cell plans are considered: The full- and half-square cell plans. To obtain capacity plots in terms of c...

In this paper we propose different backoff algorithms for different classes of users. Namely, throughput sensitive users that can support higher delays but do not support a high number of retransmissions, and delay sensitive users that need to transmit their information in a time constrained base and can support a high number of retransmissions. Th...

In this paper, three random access control mechanisms based on the well-known Slotted ALOHA, NP-CSMA, and 1P-CSMA protocols are presented. The basic idea is to limit the number of transmissions and retransmissions at high traffic loads in order to minimize collisions while keeping system stability. A new medium-access control protocol called Adapti...

CDMA and TDMA overlay has been investigated as a way to take advantage of the bandwidth available in narrowband systems. It has been demonstrated that without notch filters and ordered co-channel TDMA slots strategies, CDMA and TDMA coexistence cannot be achieved in practical situations. The use of notch filtering rejects only part of the intracell...

Theoretically the separation of CDMA and narrowband waveforms can be done through notch filters; however it has been demonstrated that the filtering techniques are not enough to eliminate the multi-cross interference problem. As a means of suppressing the interference that can not be eliminated by the use of filters this work presents a new proposa...

In this work we evaluate the reverse link coverage and capacity of a CDMA micro cellular system for voice and high data-rate (HDR) users using static simulations, dynamic simulations and analytical approaches. We study the ideal Manhattan like street pattern so the full- and the half-square cell plan are considered. To obtain coverage plots in term...

In this work, we evaluate the performance of the downlink in a CDMA cellular system with a services mix (voice and high data-rate packet). The users that arrive to the system follow a Poisson process. The data service is WWW traffic and the transmission is made through code aggregation in burst mode. The focus of this work is not only in the perfor...

In this paper the effect of antenna sectorization on the uplink user capacity of a macrocell/microcell CDMA system is studied. A "hot spot" microcell is embedded within a large macrocell and operates over the same bandwidth as the large cell. The macrocell base station uses an omnidirectional antenna and the microcell base station uses an ideal and...

A capacity evaluation method for cellular systems with CDMA is introduced. In CDMA cellular systems, the capacity of each cell depends on the actual interference produced by users supported by the other cells of the systems. This is because cell capacity is interference-limited. In this way, valid configurations of the system in terms of users per...

We evaluate the performance of the burst admission algorithms for high data-rate (HDR) packet services in the forward link of a code division multiple access (CDMA) microcellular system using a mix of static and dynamic simulation approaches. We consider the ideal Manhattan-like street pattern, so two cell plans are considered, full-square and half...

We evaluate the performance of the supplemental channels that are assigned to high data-rate users during a burst. In order to understand the impact of variation of the environment on the burst performance due to user mobility, we use a dynamic simulation approach. We study the ideal Manhattan-like street pattern and therefore two cell plans are co...

We make a performance evaluation of the air interface system EDGE (enhanced data rate for GSM evolution) introducing the adaptive traffic load (ATL) S-ALOHA as the random access protocol. The EDGE system originally considers the S-ALOHA random access protocol to let users access the network for transmitting their data packets. However, S-ALOHA beco...

In this paper we evaluate the reverse link Erlang capacity of a TDMA microcell hotspot embedded on a multiclass CDMA macrocell operating over the same bandwidth. To allow this coexistence we propose the use of ordered hunt and slots reallocation on the TDMA layer. Analytic methods are presented for computing user capacity incorporating the effects...

In this paper, the effect of antenna sectorization in the reverse link erlang capacity of a multiclass code-division multiple-access (CDMA) cellular system is studied. Traditionally, it has been considered that the capacity is multiplied by a factor equal to the number of sectors introduced. This is true only in the ideal antenna sectored system. H...

In this paper a new architecture for wireless communication networks, called intermitstations, is proposed. An intermitstations system consists of two or more non-overlapping infestations systems operating in an intermittent and sequential form, in this way, intermitstations systems spatially distribute in a time-multiplexed fashion the total syste...

Future wireless communication systems will consist of at least one network with anywhere/anytime coverage supplemented by limited coverage networks offering high speed communication services with low cost per transmitted bit, and using low power consumption portable terminals. In this paper a new system architecture for limited coverage wireless co...

This paper extends and complements a previous research where we show that the overlay of multicast CDMA and TDMA systems is possible with the assumption of an ordered hunt. In this work, we present a new scheme of overlay situation in which the cochannel TDMA slots are placed at the end of the list but with the additional assumption of a slots real...

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 mob...

In this paper we evaluate the forward link Erlang capacity of a multiclass CDMA and TDMA systems when they are overlaid. Additionally, we propose two schemes for the overlay situation, ordered hunt and slots reallocation (reallocation control model). For the ordered hunt scheme we assume that the TDMA slots are numbered 1,2,...,N_TS in a...

This article presents a mathematical analysis of the access delay in the adaptive traffic load (ATL) protocol. The basic idea of the ATL protocol is to limit the number of packet transmission for both new and backlogged users, in order to avoid collisions and keep the system stability. For this purpose, all users have an authorization probability t...

In this paper, the frequency reuse and the distributed dynamic channel assignment for microcellular networks are studied. We show that it is possible to use carriers with violation to the frequency reuse pattern with an insignificant degradation of the quality of service. As a result, a new family of distributed dynamic channel assignment algorithm...

In this paper we evaluate the reverse link Erlang capacity of a multiclass CDMA and TDMA systems when they are overlaid. We consider the Poisson nature of the arrivals in both systems and an interesting variation of the Erlang loss model used in TDMA system with the additional assumption of an ordered hunt. That is, we assume that the TDMA slots ar...

In CDMA cellular systems, all radio channels use the same frequency band, and the same radio channel can be reused in all neighboring cells. On the forward link there are at least two base stations involved in the soft handoff process, where each base station supports a forward link channel to the mobile, this produce capacity gain by macrodiversit...

The overlay of a wireless local loop system on the CDMA2000 cellular system is proposed. The CDMA2000 system uses 5, 10, 15 and 20 MHz of dispersion bandwidth and the WLL system uses 1.25 MHz of dispersion bandwidth. In this way, it is possible to have 3, 4, 8, 9, 12 and 16 frequency allocations for the WLL system depending on the different bandwid...

The forward and reverse link capacities of CDMA2000 and IS-136 are evaluated when they are overlaid. It is assumed that IS-136 support mainly voice services and that CDMA2000 support different services with different rates and quality requirements. Multicode and variable processing gain are studied. Moreover, as CDMA2000 can use 1.25 MHz and 5 MHz...

We propose an aggressive distributed dynamic channel assignment strategy (DDCA) for multirate transmission microcellular networks. To our knowledge, aggressive DDCA schemes for multi-rate transmission systems have not been considered in the literature. Our proposed strategy prioritize high-rate (new or handoff) calls over the low-rate ones with imp...

We evaluate analytically the performance of fractional channel reservation for high-rate traffic calls prioritization in TDMA and CDMA integrated services networks. We assume that low-rate traffic calls require one basic rate channel and high-rate traffic calls require m basic rate channels. In the TDMA systems, m is an integer number and in the CD...

In this paper we evaluate the reverse link capacity of direct sequence-code division multiple access (DS-CDMA) cellular system supporting multiclass services. We present an approximated analysis of the Erlang capacity, considering that blocking in CDMA occurs when the interference level reaches a predetermined level above the background noise level...

We propose a new medium access control mechanism for EDGE. This strategy employs the slotted ALOHA random multiple access based on the traffic load of the system. Slotted ALOHA reaches the maximum throughput of 36% at a normalized traffic load of 1 packet per slot transmission time. Adaptive traffic load S-ALOHA keeps the maximum throughput for nor...

The effects of antenna sectorization on the reverse link capacity of cellular CDMA systems is studied. Traditionally, the effects of ideal antenna sectorization have been considered as a multiplication factor of the same value as the number of sectors introduced. Our contribution is to study the effect of real antenna patterns on the capacity of CD...

In this work, distributed dynamic channel assignment strategies with violation to the reuse pattern using vehicular mobility information for highway microcellular environments are proposed. It is shown that, when vehicular mobility information is included in the acquisition channel policy, the outage probability degradation because of the use of ch...

A novel architecture for a microcell/macrocell cellular system is proposed. Instead of a universal frequency reuse and orthogonal sharing between layers, a “carrier reuse” distance is used in the macrocell layer. In the microcell layer, carriers that are not used in the overlaying macrocells can be used. With this architecture macrocells use hard h...

We propose a channel assignment strategy to prioritize handoff calls in multi-rate mobile microcellular networks. This strategy is based on the non-handoff failure system and employs the novel concept of intra-cluster channel reassignment. Simulation results reveal that large bandwidth traffic classes are blocked or forced to terminate more often t...

Many dynamic channel assignment (DCA) algorithms have been developed, however, all of these proposed algorithms are targeted for single rate cellular networks. Up to now, very little research has been done for multi-rate cellular systems that have integrated services, i.e., voice, data, video, etc. We evaluate the performance of the maximum packing...

A fractional channel reservation scheme is proposed. In conventional channel reservation schemes, the number of channels reserved for handoff calls has always been an integer. The proposed fractional channel reservation algorithm can be used to finely control the communication service quality. By varying the number of reserved channels for handoff...

The performance of a Manhattan like microcellular system with multiple reuse patterns (MRP) is evaluated. The system capacity and the outage probability are calculated. The outage probability, the probability of receiving an inadequate signal-to-interference ratio, is evaluated considering log-normal shadowing. The effects of the reuse factor, the...

In this work, moving direction distributed dynamic channel assignment (DDCA) strategies with violation to the reuse pattern (VD-DDCA) for highway microcellular systems are proposed. It is shown that the outage probability degradation caused by one violation to the reuse pattern (VRP) when moving direction (MD) strategies are used in the acquisition...

A new distributed dynamic channel assignment scheme with implicit channel reservation for handoff prioritisation is proposed. This scheme reduces the degree of computation and communications among base stations required for channel reservation and achieves a capacity similar to that of the maximum packing algorithm. For 40 total channels, the propo...

We show that due to the particular propagation conditions in urban microcellular environments it is possible to use channels with violation to the frequency reuse pattern for handoff prioritization with an insignificant degradation on the quality of service. This is possible because we restrict the use of channels with violation to the reuse patter...

The Erlang capacity per cell and per unit area in a CDMA urban microcellular environment are evaluated. Two different cell plans are considered where the communication between the base station and the mobile unit always occurs in line-of-sight condition: the full and the half square cell plans. We obtain analytical expressions for the Erlang capaci...

Personal Access Communications System-Unlicensed B (PACS-UB) is a standard intended to operate in the band allocated for Unlicensed Personal Communication Services (UPCS) in the U.S. Because of this, the systems working according to PACS-UB, have to comply with the etiquette rules defined by FCC for interoperability in the UPCS band. These rules, a...

In this paper, the effect of the hard and soft handoff on the reverse link capacity for a CDMA Manhattan like microcellular system is evaluated. We obtain analytical expressions for the relative other-cell interference factor as a function of the breakpoint, the cell radio, the variance of the random variation and the propagation path loss exponent...

We study the impact of the breakpoint distance on the capacity of a Manhattan like microcellular CDMA system. We consider the other-cell interference as a Gaussian random variable and we obtain its mean and variance as a function of the breakpoint distance. Also, the distribution of the BER as function of the breakpoint distance, the cell radio, th...

In this paper, a new family of distributed dynamic channel assignment (DDCA) algorithms is presented, the DDCA with violation to the reuse pattern (DDCA with VRP). The DDCA algorithms with VRP allow to use carriers with at most one violation to the reuse pattern, under the restriction that both cells using simultaneously the same carrier must be th...

The Personal Access Communications System-Unlicensed B (PACS-UB) is a standard intended to operate in the (1920-1930 MHz) band allocated for Unlicensed Personal Communication Services (UPCS) in the US. The access of portables in PACS-UB is carried out based on measurements. This paper presents the analytical derivation of the downlink signal to int...

In this paper the frequency reuse problem in microcellular systems is studied. It is shown that due to the particular propagation conditions in microcellular environments, the frequency reuse pattern can tolerate one or more violations. Taking into account the possibility of admitting one violation to the reuse pattern, a new concept of available c...

The compact pattern with maximised channel borrowing (CPMCB), a dynamic channel assignment strategy (DCA), is evaluated for the pan-European GSM system. This DCA algorithm takes advantage of the compact patterns to decrease the blocking probability by always assigning a channel to a pattern that improves the system performance. Channel borrowing an...

The compact pattern with maximized channel borrowing (CPMCB), a new dynamic channel assignment strategy (DCA), is proposed. This new DCA algorithm takes advantage of the compact patterns to decrease the blocking probability by always assigning a channel to a pattern that improves the system performance. Channel borrowing and channel reallocation st...

Compact pattern with maximised channel borrowing (CPMCB), a novel dynamic channel assignment strategy (DCA), provides efficient spectrum reuse in cellular mobile networks. Numerical examples show 8% more traffic carrying capacity than borrowing with directional channel locking (BDCL), and ~80% more compared with the fixed channel assignment strateg...

Traffic capacity improvement is a strong necessity of cellular systems. One of the main techniques to increase capacity is the utilization of microcells. However, as cells are reduced, handoff rates are increased. In this paper the influence of the handoff process in the channel holding time is studied. The channel holding time is defined as the ti...

An interference limited environment is proposed for the evaluation of channel assignment strategies for digital systems based in the IS-54 standard. This environment consists of two rings of co-channel interference cells (133 cells) with uniform and nonuniform traffic distribution. At call initiation the C/I ratio is evaluated. A minimum C/I value...