Optical Wireless Communication (OWC) and Radio Frequency (RF) heterogeneous networks (HetNets) offer enhanced connectivity by leveraging the complementary advantages of both technologies. Efficient resource allocation in OWC/RF HetNets requires addressing transmission power and coverage disparities, which impact efficiency and service quality, posing challenges to seamless integration. This paper addresses the transmission power allocation problem in OWC/RF HetNets by formulating it as a multi-objective optimization framework. The objectives aim to minimize transmission power for OWC and RF links while maximizing dual-mode data rates. To this end, we propose a novel Q-learning-based framework tailored to multi-objective optimization. Unlike conventional reinforcement learning approaches that aggregate reward functions into a single scalar measure, our method treats reward functions independently by maintaining distinct Q-values for each state-action-reward tuple. Additionally, we introduce an innovative action selection mechanism that simultaneously evaluates multiple Q-values, ensuring balanced decision-making across competing objectives. Extensive simulations validate the proposed framework, demonstrating superior convergence speed, energy efficiency, and adaptability to dynamic network conditions compared to conventional Q-learning methods.

This paper presents a novel multi-attribute decision-making approach for managing handovers in Optical Wireless Communication/Radio Frequency Heterogeneous Networks (OWC/RF HetNets). The proposed method systematically evaluates potential Access Points (APs) using multiple criteria, including fixed and variable handover costs, the ratio of the node's data rate demand to the achievable rate from APs, and the ratio of the utilized capacity of APs. Using local parameters, nodes assess these attributes over a finite future horizon and construct a decision matrix. The VIKOR method is then applied to decide whether to initiate a handover to a new AP or remain connected to the current one. Simulation results show that the proposed decentralized scheme effectively manages handovers, leading to improved load balancing and reduced handover latency in OWC/RF HetNets.

The sustainable design of Internet of Things (IoT) networks encompasses considerations related to energy efficiency and autonomy as well as considerations related to reliable communications, ensuring no energy is wasted on undelivered data. Under these considerations, this work proposes the design and implementation of energy-efficient Bluetooth Low Energy (BLE) and Light-based IoT (LIoT) batteryless IoT sensor nodes powered by an indoor light Energy Harvesting Unit (EHU). Our design intends to integrate these nodes into a sensing network to improve its reliability by combining both technologies and taking advantage of their features. The nodes incorporate state-of-theart components, such as low-power sensors and efficient System-on-Chips (SoCs). Moreover, we design a strategy for adaptive switching between active and sleep cycles as a function of the available energy, allowing the IoT nodes to continuously operate without batteries. Our results show that by adapting the duty cycle of the BLE and LIoT nodes depending on the environment’s light intensity, we can ensure a continuous and reliable node operation. In particular, measurements show that our proposed BLE and LIoT node designs are able to communicate with an IoT gateway in a bidirectional way, every 19.3 and 624.6 seconds, respectively, in an energy-autonomous and reliable manner.

Since the last decade, researchers have been continuously trying to implement and evaluate the performance of Drone Assisted Vehicular Network (DAVN). A DAVN efficiently integrates the networking and communication technologies of drones with connected vehicles. DAVNs have a huge potential to offer a wide range of features for Intelligent Transport Systems (ITS) applications to improve traffic safety on roads. In this paper, we first discuss the architecture of a DAVN and outline its potential services for vehicular networks. Drones cooperate with infrastructure and vehicles to improve Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) network coverage, data collection capability, and efficiency of communication interworking. In this paper, we demonstrate the DAVN concept with regard to Drone-to-Vehicle (D2V) and Drone-to-Infrastructure (D2I) communications utilizing road meteorological data exchange. To perform these pilot scenarios, we use real-time weather and traffic data collected during our pilot measurements in Northern Finland. The executed and generated test scenarios are added to Wireshark and NS-2 (Network Simulators) to evaluate the performance of ITS-G5 and 5G Test Network (5GTN). The performance evaluation for DAVN is carried out by considering the following parameters: end-to-end delay, packet delivery ratio (PDR), packet loss and average throughput. Our results revealed that ITS-G5 performs better and more efficiently than 5G in D2V PDR scenarios, and 5G performs well in D2I PDR scenarios. Moreover, the 5G network presents better performance in the average throughput and D2I (in our case drone-to-RWS (Road-Weather-Station)) delay scenario in contrast to ITS-G5, and this is due to vehicles, haphazard nature of test track and the distance between the cars.

As internet of things (IoT)-based wireless personal area networks (WPAN) get more popular, visible light communication (VLC) offers unique advantages over radio frequency (RF) communication, such as unrestricted reusable spectrum and high security. Additionally, visible light can carry both signals and optical power, making it a useful medium for exchanging information and energy between network nodes. A VLC-based wireless personal area network (WPAN) concept for light-based energy autonomous IoT is proposed in this paper, which can share both data and energy between nodes. The network uses photovoltaic (PV) based energy harvesting for operation while sharing excess energy between nodes to increase efficiency. Performance of the main concept of the network is evaluated and discussed in the paper. In the future, this kind of network will enable self-sustaining IoT networks.

5G mobile communications have received enormous attention from the communication community, in particular for applications requiring low latency, as in Vehicle-to-vehicle (V2V) and Vehicle-to-infrastructure (V2I) communications in Intelligent Transport systems (ITS). 5G has already been studied through simulations and pilot use-cases in vehicular ad-hoc networks (VANETs) scenarios. Currently, the other prominent wireless technology is ITS-G5, a networking technology standardized by the European Telecommunications Standards Institute (ETSI) for vehicular communications. By integrating the ITS-G5 and 4G/5G networks, the advantages of both systems can be readily exploited by the V2I, V2V and V2X systems. In this article, we have investigated low-latency vehicular communications considering the combined operation of ITS-G5 and 5G networks. We specifically analyze the seamless handover process between ITS-G5 and 5G Test Network (5GTN) by conducting field measurements at the Finnish Meteorological Institute (FMI) test track in Northern Finland. We analyze the latency and packet drop during the seamless hand-off between the two wireless technologies. This article also discusses an advanced road weather services architecture that assures stable communication links for heterogeneous networking technologies. Results show that the heterogeneous network considerably improves the load balancing and communication link availability between VANETs and infrastructure.

In recent years, the vehicular ad hoc networking (VANET) concept has supported the development of emerging safety related applications for vehicles based on cooperative awareness between vehicles. This cooperative awareness can be achieved by exploiting wireless sensors and technologies to transmit periodic messages to neighboring vehicles. These messages normally contain information regarding vehicles, such as position, speed, distance between vehicles, etc. For the transfer of safety messages, Wi-Fi and the suit of IEEE 802.11p/WAVE protocols were commonly used initially but now cellular-based LTE and 5G are the emerging technologies for VANETs. In this paper, a comparison is performed considering the European ITS-G5 standard, Wi-Fi, LTE and 5G by exchanging safety messages in VANETs. We have exchanged real-time road weather and traffic observation data to evaluate the performance of the aforementioned wireless technologies in terms of successful message delivery probability. Our results reveal that due to weak communication links and the lack of line of sight (LOS) communication for Vehicle to Infrastructure (V2I) and Vehicle to Vehicle (V2V) scenarios, Wi-Fi and 802.11p are outperformed by LTE and 5G networks.

In the near future, with the development of 5G NR, a massive number of IoT nodes are expected to come online. Acquiring bandwidth from an overcrowded licensed radio frequency spectrum as well as overcoming battery life constraints will become the main challenges for these IoT based devices. As a promising solution for the above challenges, this work provides a feasibility study and an implementation framework for a visible light communication-based energy-autonomous IoT node. This work proposes the use of printed electronic technology to minimize the physical characteristics and cost of the IoT node. In the future, energy-autonomous IoT nodes could be available virtually on any surface. Whenever the node is exposed to light, it will be connected to internet.

In recent years, the research community has shown increasingly interest in the study, design and implementation of DAVNs (Drone-assisted Vehicular-Network). DAVN can play a crucial role to provide a broad range of vital characteristics for Intelligent Transport Systems (ITS) applications to enhance the road traffic safety. A DAVN provides a dynamic platform by effectively combining the ground networks, namely Connected Vehicles (CV) and aerial communication technologies of drones. In DAVN, due to the small sizes of drones, payload constraints as well as capabilities and flight time limitations, cooperating with traffic infrastructure and vehicles is very important. DAVNs help to improve the Vehicle-to-Infrastructure (V2I) and Vehicle-to-Vehicle (V2V) communication range, the information gathering capability, and the efficiency of vehicular networking. In this paper, we develop a novel cooperative DAVN architecture consisting of drones, vehicles, Road Weather Stations (RWS), on-board embedded sensors, processing entities, Global-Positioning-System (GPS), and communication capabilities. We use real-time field measurements of V2V and V2I communications considering weather and vehicular traffic information for drone assisted vehicular communication simulations in Network Simulator-2 (NS-2). DAVN simulations are carried out based on measurements on a real environment (1.7km long test track) at the Finnish Meteorological Institute (FMI) in Sodankylä, Finland. The performance of DAVN was evaluated by considering three parameters: packet loss, network latency and average throughput. Simulation results revealed that ITS-G5 performance is stable in short range, but in long range DAVN, the 5G Test Network (5GTN) and its 4G feature outperformed ITS-G5. Moreover, we identified key challenges in the design and implementation of DAVNs in real environments.

Visible light communication (VLC) is an emerging optical wireless technology which has the potential to complement existing radio frequency (RF) communication systems aiming at exploiting the advantages of both networks. The concept of such complementing as hybrid VLC/RF systems is well understood theoretically but not much has been done on practical realization. In this paper, we report implementation details of a hybrid VLC/RF point-to-point system, where two nodes are connected with each other via VLC and RF links. In this implementation, we consider VLC link as primary link therefore it will always be an active link whenever it is available. Nodes are capable of vertical handover between two types of communication links in case of primary (VLC) link failure and restoration. The VLC link state plays important role so we describe a continuous link monitoring protocol and criteria for switching between VLC and RF links. To switch between two links a Linux kernel bonding driver has been used. A simple link monitoring protocol has been implemented for VLC link state and it is passed continuously to bonding driver for decision. Performance of this system has been evaluated for user datagram protocol (UDP) content distribution while handover. Hence, a simple hybrid system capable of handover between VLC and RF links has been achieved.

In this paper, a novel differential chaotic bit-interleaved coded modulation (DC-BICM) system is proposed for band-limited transmission. This system combines protograph-based low density parity check codes with constellation-based M-ary differential chaos shift keying (DCSK) modulation by one bitwise interleaving. Bit error rate simulation results show that the system has higher coding gain compared with the constellation-based M-ary DCSK modulation system with the same spectral efficiency over multipath Rayleigh fading channels. At the same time, several simulations and P-EXIT analysis are used to analyze the performance of the proposed system. It is found that there is a lot of room for optimization of the system by comparing decoding thresholds and simulation results. Moreover, the system with only partial channel state information has better performance and lower complexity compared with the traditional bit-interleaved coded modulation (BICM) directsequence-spread-spectrum system. As a result, the DC-BICM system is a good candidate for band-limited transmission.

In next-generation wireless networks, device-to-device (D2D) communication represents a feasible way for mobile users to offload their cellular traffic demand without extra costs for deploying additional infrastructure from the network operators. Cellular (e.g., 3GPP LTE) network assistance can automate user/service discovery and connection establishment procedures, as well as enable secure D2D connectivity between proximate users. Currently, assisted direct connectivity is only available in the form of unlicensed-band protocols (e.g., WiFi Direct), which motivates research on understanding its practical limitations with realistic distributions of users and content. Whereas there are concerns that D2D communication alone may not be efficient due to limited content availability, in this paper, we advocate the use of network coding to upgrade assisted proximate communication and make it realize its full potential. In particular, we demonstrate that even simpler network coding techniques are capable to significantly improve the degrees of content availability for communicating users and thus enhance offloading performance under realistic constraints. Inspired by the recent popularity of wireless content distribution systems over D2D caches, we contribute a practical methodology for assisted data caching and distribution, mindful of the state-of-the-art D2D technology.

Thanks to the smart device revolution, modern wireless devices have increased computational/storage capabilities and can also support for multiple network interfaces such as cellular and WiFi interfaces. Intelligent utilization of multiple network interfaces can address the problem of cellular traffic congestion and it can also increase the frequency resources of cellular networks. Cooperative content distribution (CCD) is one such technique that can be performed by using multiple wireless interfaces. In CCD, a device receives content from a base station on its cellular interface and distributes it to other devices in its vicinity through another wireless interface such as WiFi. However, due to the broadcast nature of the secondary links such as WiFi, even a single bad link can serve as a bottleneck in terms of the CCD performance. To address this problem, in this paper, we propose a device selection method for CCD that takes into account both the primary (cellular) and secondary link (WiFi/short-range) network interfaces. The proposed method incurs little overhead as it utilizes information such as acknowledgement of data packets, that already exists in the network. We evaluate and compare (with the other content delivery methods) the performance of the proposed method in terms of: number of carriers utilized by a cellular base station (BS); average bits-per-Joule performance; and the average time required to deliver a content file. Moreover, we also take into account the impact of the presence of independent competing/interfering links (such as competing users in the unlicensed band) on the performance of the proposed method.

In this paper, we consider downlink resource allocation of a cellular user to group of device-to-device (D2D) communication pair to enhance the overall system throughput and achieve higher spectral efficiency in mobile cloud. A mobile cloud can be defined as an opportunistic cooperative cluster of wireless devices in close proximity which are capable to communicate to other devices while preserving their connection to an overlay cellular access network (i.e., eNB), simultaneously. Thus this study considers D2D communications from a novel and wider perspective, assuming that multiple D2D communication links are simultaneously supported. We model, formulate and analyze the overall throughput of the mobile cloud as the function of distance between communication devices when the D2D pairs communicate in cellular, dedicated and reuse modes. In cellular and dedicated modes there is no severe intra-cell interference but for the reuse mode we propose an innovative and practical downlink resource allocation mechanism to coordinate the interferences and maximize the system sum-rate when several D2D pairs communicate by reusing the resources of a cellular user. In fact, the eNB as the centralized decision-maker selects a cellular user equipment (UE) and group of D2D pairs to communicate by reusing the downlink resources of the selected cellular UE while it guarantees the SINR at both the cellular and D2D receivers. Numerical results show that by exploiting the proposed mechanism we can achieve the aforementioned goals.

In this work, we will study the performance of combined wireless local area network (WLAN) and visible light communication (VLC) in indoor environment by taking into account the data download on move scenario. In this combined networks both WLAN, and VLC are characterized by their data rates and communication range. In VLC, short range spotlighting cell is considered for high data rate region acts as VLC hotspot. WLAN is used for continuous connectivity and increasing coverage range of hybrid WLAN-VLC hotspot. Moreover, mobility issues of mobile users have also been considered in the performance of hybrid WLAN-VLC hotspot. Simulations have been performed to evaluate the performance of such network for data downloading on move scenario by taking into account performance metric such as file size. Simulation results reveal that there is impact of mobile user velocity and number of VLC hotspots present in the considered service area of hybrid WLAN-VLC hotspot.

Smartphones can be viewed as resource pools capable of communicating with their outside world. Such communication capabilities provide unique opportunity for sharing resources, which would result in new possibilities for end users. In this paper, we present a new framework designed for managing mobile local networks, also referred to as Mobile Clouds. In this framework, mobility of nodes is managed by selecting one leader for each cloud, which is responsible for all cloud-level decisions, as well as processing all incoming data from other users. We also evaluate and discuss our proposed framework under different scenarios.

In this paper, we investigate cooperative architectures and cloud formation mechanisms within the concept of mobile clouds, where multi-standard multi-radio devices in close proximity communicate to each other over short-range radio links while preserving connectivity to the overlay cellular network. Four architecture approaches are considered, namely a central cellular controlled, a cloud leader based as well as two novel hybrid schemes. We develop models and derive analytical expressions for the performance of the studied architectures. The performance of cloud formation mechanisms for these architectures is then compared. We show that the proposed hybrid mechanisms outperform the basic approaches in terms of control message overhead, cloud formation latency and energy consumption.

This paper compares the energy and time needed to convey one information unit from source to destination using multi hop networks versus overlay networks. For a set of realistic parameters the paper will show that multi hopping with more than 50 relays will need more time than the overlay network and with respect of energy the usage of more than 6 relays is using more energy than the overlay network. The paper underlines the importance of the idle power value for such calculations.

Future wireless access networks, characterized by a large number of small cells densely distributed in metropolitan area, are likely to be the dominating form of future wireless communications. It is expected that the dynamic spectrum access (DSA) enabled by cognitive radio (CR) technologies will act as a key for their success. Considering the high cell density and the large size of network, the spectrum coexistence will be a prominent problem in future wireless access networks. In this paper we study the spectrum self-coexistence of DSA based wireless access networks. The objective is to improve the spectrum utilization among densely distributed cells. To achieve this, topology-aware distributed algorithms are proposed for mobile terminal (MT) association and access point (AP) channel selection. The proposed algorithms enable self-coordination of spectrum in studied networks. The simulation study shows the efficiency of distributed solutions to solve the spectrum coexistence problem in proposed networks.

In this paper we develop and analyze energy- efficient cooperative techniques for multimedia streaming applications in wireless networks. The concept of combined cellular- SR network architecture is coupled here with different video coding schemes for the goal of achieving robust transmission over wireless channels and energy saving. The strategies are analyzed in different technology settings, showing promising power saving potentials in comparison to the state-of-the-art non-cooperative operation.

The standard IEEE 802.16 was originally conceived for targeting local and metropolitan area networks, for relatively small link distances. However, the significant deployment of novel wireless-based applications as well as the availability of advanced transmission techniques has suggested a possible extension of the standard-based systems to mountainous and isolated areas. From the propagation point of view, those demanding scenarios result in to non-line-of-sight, long delay spread, and very rich scattering radio environments. Nowadays, no channel models proposed in the literature are suitable for modeling 3.5 GHz transmission in such demanding scenarios. In this paper we propose a possible solution by analyzing and modifying the IST-WINNER model. According to the simulations, the novel channel model characterizes the strong peaks due to the reflection from a mountain and the interfering paths due to near scatterers. The combination of these paths creates a long delay spread that can be fatal for OFDM-based systems. Finally, in order to show the impact of the challenging scenario on the system performance, we present the results related to a system-level simulation using beamforming/MIMO techniques.

In this paper we advocate to exploit terminal cooperation to stabilize IP communication using header compression. The terminal cooperation is based on direct communication between terminals using short range communication and simultaneously being connected to the cellular service access point. The short range link is than used to provide first aid information to heal the decompressor state of the neighboring node in case of a packet loss on the cellular link. IP header compression schemes are used to increase the spectral and power efficiency loosing robustness of the communication compared to the uncompressed version. By introducing the terminal cooperation supporting header compression the robustness is increased. Within this article we will show that header compression should be applied to reduce the energy consumption of the terminals and moreover the header compression should be supported by cooperation to increase the robustness in terms of a decreased packet loss rate.

This paper reports the results of a measurement campaign on the connectivity level of mobile devices using Bluetooth (BT) to form cooperative mobile mesh networks. Such mobile mesh networks composed of mobile devices are the basis for any peer-to-peer communication like wireless grids or social networks. The results represent typically worst-case situations, as more and more people tend to switch off their short-range technology due to the battery consumption and the possible attacks. We explore typical public places like airports, convention centers, shopping malls and bars and extract from them some statistics of the size of the mesh network and type of constituent nodes. This information is essential for analyzing and devising cooperative strategies among the terminals of mesh networks in different scenarios.

This paper introduces power saving strategies for cooperative wireless communication systems. The described scenario focuses on IP-services over DVB-H networks showing the strength of non-altruistic cooperation between mobile devices. The envisioned cooperation is based on cellular reception of data, which is then shared among mobile devices within each others' proximity over short-range links. As the state-of-the-art, we use Bluetooth technology for the short-range link communication in this cooperative scheme. In this paper, three topology based cooperative algorithms for the short-range link communication are designed. Then numerical results show that a power saving gain of over 50% can be achieved by cooperative networking of three mobile terminals in fully cooperating mode.

In this paper we introduce a novel header compression technique for parallel channels as they are found in meshed networks. The approach introduced advocates the cooperative behavior of parallel channels to maintain the compression state on sender and receiver side. The general concept as well as one particular implementation are shown. Our approach is characterized by no need of a feedback channel and a low complexity of a compression strategy. By means of analytical study combined with our testbed results we show the performance of the introduced approach. The designing goals were to have a low complex, highly efficient and also robust header compression dealing with the characteristics of the wireless channel. As a first result we can show that for independent error pattern a number of three cooperative channels achieves both robustness and efficiency for a wide range of errors.

In this paper we advocate the use of multiple base stations for providing wireless link to an OFDM-based terminal and thus obtain macro diversity, in particular site diversity. The wireless link to a terminal is defined through a subset of sub-carriers that is optimized in a greedy manner over the union of base stations. The wireless terminal is unaware of how many and which base stations are providing its allocated set of sub-carrier, which simplifies the terminal design. We give an analytical comparison of our approach to the conventional solutions. The results show that the proposed schemes with multiple base stations can outperform the single base station case, while keeping the complexity of the wireless terminal unchanged. We further evaluate our schemes by considering minimize signalling over the air interface.

4G wireless communication networks are characterized by the need to support heterogenous terminals differing in size, display, battery, computational power, etc. For efficient usage of the wireless spectrum all devices should be served by the same spectrum instead of allocating spectra dedicated to the different terminal classes. This feature is naturally supported when the source coding of the traffic is done as a multiple description coding. The restoration quality of the information source is proportional to the quantity of the descriptors used in the restoration process. Hence, terminals with less capabilities may simply discard or not receive some of the descriptors, while high class terminals try to receive all information. In the case of partial reception of descriptors the performance can be improved by selection strategies for the descriptors. We advocate the usage of new descriptor selection schemes for multiple description coded services. The proposed schemes differ with respect to the availability of a feedback channel. All solutions are terminal oriented and are beneficial in the design of terminals that have robust and high quality services. Furthermore, our approaches inherently achieve fairness among different terminals. As an example of our results for video communication, we can show gains of 4 dB when the proposed approach is utilized in the system.

In this paper we propose and analyze an adaptive spatial modulation scheme for MIMO-OFDM systems which adaptively and optimally selects one of the following transmission modes: diversity, spatial multiplexing and a hybrid combination of these two modes. Two criterias are used for mode selection, namely, the minimum Euclidean distance and a simple threshold based stochastic method exploiting channel quality estimations. We consider practically implementable antenna configuration with four transmit antennas and two or four receive antennas. Simulation results show that considerable BER performance gains can be obtained by the adaptive spatial modulation system, as compared with systems based on fixed modulation schemes.

In this paper, we investigate code acquisition in the delay and angular domain in environments where interference and noise are nonuniformly distributed in the spatial (angular) domain. It is seen that performance is clearly degraded by the presence of nonuniform spatial distributions of interference. The degree of impairment is related to the actual shape of the distribution and becomes more significant when large amounts of interfering power are concentrated in one or more angular directions. As compared to a reference case with a uniform distribution of equivalent interfering power, the mean acquisition time could increase by factors of up to four. Some effective approaches to compensate for the loss of performance due to the uneven nature of interference are also studied. First, the effect of search strategies in the delay and angular domains on acquisition performance is assessed. A searching algorithm up-ranking angular cells according to the amount of associated interference is proposed as one solution to reduce the performance gap. It is shown that applying this search strategy can considerably reduce the mean acquisition time. Finally, two adaptive schemes based on setting integration times or threshold values according to the level of interference prevailing in each angular cell, are discussed. The former approach returns performance figures similar to those obtained with the uniform equivalent interference distribution while the latter provide moderate performance gains.

A closed-loop method combining N-out-of-M antenna selection and space-time block coding from the selected antennas is proposed and studied in this paper. Performance is evaluated for WCDMA parameters in both frequency nonselective Rayleigh fading channels and in frequency selective (Vehicular A) channels. Operation in intra- and inter-cell dominant interference scenarios is considered. Numerical results show that the additional antenna selection procedure brings a supplementary uncoded BER performance improvement in the range of approximately 2-3.5 dB for flat-fading channels and 0.8-1.5 dB for frequency selective channels (@BER=12%). A suboptimum selection scheme requiring only a single bit for antenna selection is also presented. In addition, the impact on performance of errors in the feedback channel is investigated in this paper.

We present models for the code acquisition process in RAKE receivers. These models include multipath diversity, multiple transmitter (base station or satellite) diversity, and multiple access interference generated by other users in the network. This results in a different probability of false alarm for each cell of the code delay uncertainty region. The analysis is based on signal flow graph theory. By using these models, we elaborate different strategies for RAKE receiver synchronization and derive exact closed-form results for the average acquisition time. These strategies differ in how they organize initial (first RAKE finger) and postinitial search algorithms. If the channel is known, the initial synchronization may organize a parallel search for all fingers simultaneously by a proper set up of the local correlators' mutual delays. If not, then a serial search of different segments (partitioned among the different fingers) can be organized. In the postinitial search, sequential or random initializations are possible. A set of approximations is also included for practical applications where a quick assessment of the system performance is needed.

The extension of conventional delay-domain code acquisition to the angular domain is explored. The uncertainty region is partitioned into a number of delay and angular cells. In single-path channels where the interference is modeled as temporarily and spatially white, there exists an optimum number of angular cells minimizing the mean acquisition time. Mean acquisition times up to three times shorter can be attained with the two-dimensional approach. A rather similar behavior is in general found in Lth-order equal amplitude multipath channels, where paths are contiguous in the delay or angular domains. The strategy employed to search through the uncertainty region may have a considerable impact on acquisition performance. The results reveal that the search should proceed not in the direction of the multipath spread but in the other available domain. Proper selection of the search strategy can reduce the synchronization time by a factor of up to two. Two-dimensional code acquisition in scenarios with spatially nonuniform interference is also investigated. In general, the acquisition performance is degraded by the presence of nonuniform interference in the angular domain.

In this paper, we discuss modeling of the serial code acquisition process in a code division multiple access (CDMA) network. Due to multiple access interference (MAI), the process is characterized by a different probability of signal detection P/sub D/ and probability of a false alarm P/sub FA/ in each cell of the code delay uncertainty region. We derive exact expressions for average code acquisition time and its variance. In addition to this, we also present several useful approximations, which enable easy engineering use of these results for practical applications in future Universal Mobile Telecommunications System (UMTS) solutions. Numerical results based on this analysis are used for decision threshold optimization in code acquisition process for asynchronous CDMA networks.

We present a model of serial code acquisition process in code-division multiple-access networks. The difference between this model and the existing work is in using the assumption that in each cell of delay uncertainty region the probability of false alarm, is different. This is caused by the fact that in each cell cross correlations between the local code and the codes used by the other users in the network are different. A closed-form expression for the average acquisition time is derived and discussed.