This paper investigates multi-target detection in an integrated sensing and communication (ISAC) system within a cell-free massive MIMO (CF-mMIMO) framework. We adopt a user-centric approach for communication user equipments (UEs) and a distributed sensing approach for multi-target detection. A heuristic access point (AP) mode selection algorithm and a channel-aware distributed sensing scheme are proposed, where local measurements at receive APs (RX-APs) are weighted based on the received signal’s signal-to-interference ratio (SIR). A maximum a posteriori ratio test (MAPRT) detector is applied under two awareness levels at RX-APs. To balance the communication-sensing trade-off, we develop a power allocation algorithm to jointly maximize the minimum detection probability and communication signal-to-interference-plus-noise ratio (SINR) while satisfying power constraints. The proposed scheme outperforms non-weighted methods. Adding test statistics from more RX-APs can degrade sensing performance due to weaker channels, but this effect can be mitigated by optimizing the weighting exponent. Additionally, assigning more sensing RX-APs to a sensing area results in approximately 10dB loss in minimum communication SINR due to limited communication resources.

Reliable wireless communication is crucial for the interconnected manufacturing systems of Industry 4.0. However, the dense distribution of stations (STAs) and obstacles such as concrete walls and machinery can adversely affect radio performance. Our study investigates the performance of Legacy Wi-Fi and Wi-Fi 6 in a factory through simulations. A ray-tracing-based propagation model is used to account for the challenging radio environment. Based on this, we apply Access Point (AP) grouping strategies to assign the constrained Wi-Fi spectrum in the factory. Multiple traffic types are simulated within the digital twin factory model to evaluate the key performance indicators (KPIs). Our findings show that Wi-Fi 6 significantly reduces Round Trip Time (RTT) compared to Legacy Wi-Fi, though increased bandwidth can lead to higher co-channel interference. The analysis also indicates the difficulty of optimizing Wi-Fi performance in industrial scenarios due to the multiplicity of influencing factors and the complexity of their correlation.

This paper studies integrated sensing and communication (ISAC) in the downlink of a cell-free massive multiple-input multiple-output (MIMO) system with multi-static sensing and ultra-reliable low-latency communication (URLLC) users. We propose a successive convex approximation-based power allocation algorithm that maximizes energy efficiency while satisfying the sensing and URLLC requirements. In addition, we provide a new definition for network availability, which accounts for both sensing and URLLC requirements. The impact of blocklength, sensing requirement, and required reliability as a function of decoding error probability on network availability and energy ef-ficiency is investigated. The proposed power allocation algorithm is compared to a communication-centric approach where only the URLLC requirement is considered. It is shown that the URLLC-only approach is incapable of meeting sensing requirements, while the proposed ISAC algorithm fulfills both sensing and URLLC requirements, albeit with an associated increase in energy consumption. This increment can be reduced up to 75% by utilizing additional symbols for sensing. It is also demonstrated that larger blocklengths enhance network availability and offer greater robustness against stringent reliability requirements.

This paper studies an integrated sensing and communication (ISAC) system within a centralized cell-free massive MIMO (multiple-input multiple-output) network for target detection. ISAC transmit access points serve the user equipments in the downlink and optionally steer a beam toward the target in a multi-static sensing framework. A maximum a posteriori ratio test detector is developed for target detection in the presence of clutter, so-called target-free signals. Additionally, sensing spectral efficiency (SE) is introduced as a key metric, capturing the impact of resource utilization in ISAC. A power allocation algorithm is proposed to maximize the sensing signal-to-interference-plus-noise ratio while ensuring minimum communication requirements. Two ISAC configurations are studied: utilizing existing communication beams for sensing and using additional sensing beams. The proposed algorithm’s efficiency is investigated in realistic and idealistic scenarios, corresponding to the presence and absence of the target-free channels, respectively. Despite performance degradation in the presence of target-free channels, the proposed algorithm outperforms the interference-unaware benchmark, leveraging clutter statistics. Comparisons with a fully communication-centric algorithm reveal superior performance in both cluttered and clutter-free environments. The incorporation of an extra sensing beam enhances detection performance for lower radar cross-section variances. Moreover, the results demonstrate the effectiveness of the integrated operation of sensing and communication compared to an orthogonal resource-sharing approach.

This paper studies a joint communication and sensing (JCAS) system with downlink communication and multi-static sensing for single-target detection in a cloud radio access network architecture. A centralized operation of cell-free massive MIMO is considered for communication and sensing purposes. The JCAS transmit access points (APs) jointly serve the user equipments (UEs) and optionally steer a beam towards the target. A maximum a posteriori ratio test detector is derived to detect the target using signals received at distributed APs. We propose a power allocation algorithm to maximize the sensing signal-to-noise ratio under the condition that a minimal signal-to-interference-plus-noise ratio value for each UE is guaranteed. Nu-merical results show that, compared to the fully communication-centric power allocation, the detection probability under a certain false alarm probability can be increased significantly by the proposed algorithm for both JCAS setups: i) using additional sensing symbols or ii) using only existing communication symbols.

Feasibility of using unlicensed spectrum for ultra reliable low latency communications (URLLC) is still a question for beyond 5G wireless networks. Low latency access to the channel and efficiently sharing spectrum among the multiple users are the main requirements for exploiting unlicensed spectrum for URLLC. Listen before talk and back-off procedures implemented to avoid the collisions in channel access hinder the low latency communication. In this paper, we propose a novel low-latency medium access control (MAC) scheme based on the collision resolution for a pairwise random wireless network. We use geometric sequence decomposition for collision resolution among the competing users. This enables the system to tackle collisions and thus removing the need for carrier sensing and back-off procedures. This saves time in obtaining access to the channel and improves the efficiency of the system. We implement our approach in the synchronized time slotted system and show that it yields significant improvement over existing MAC schemes.

Abstract Cooperation of co‐located mobile network operators can provide potential benefits for the capacity expansion without further densification of radio nodes. However, such benefits need to be scrutinised for coexisting cloud radio access network (C‐RAN) operators because the inter‐operator cooperation may compromise the superb interference coordination capability that each C‐RAN has. Furthermore, altering C‐RAN infrastructure for the cooperation incurs a high investment cost. In this paper, quantitative gain of inter‐operator coordination strategies is evaluated to provide the C‐RAN operators with a guideline on their cooperation decisions. The coordination strategies encompass dynamic user association and the spectrum sharing which aim at maximising the total user throughput. A heuristic algorithm is proposed that reduces the computational burden of the coordination significantly. Numerical results suggest that the inter‐operator cooperation is beneficial particularly when the network size of each operator tends to be highly asymmetric. It is also verified that the users who belong to smaller network attain more coordination gains.

This paper presents a computationally efficient technique for decomposing non-orthogonally superposed k geometric sequences. The method, which is named as geometric sequence decomposition with k-simplexes transform (GSD-ST), is based on the concept of transforming an observed sequence to multiple k-simplexes in a virtual k-dimensional space and correlating the volumes of the transformed simplexes. Hence, GSD-ST turns the problem of decomposing k geometric sequences into one of solving a k-th order polynomial equation. Our technique has significance for wireless communications because sampled points of a radio wave comprise a geometric sequence. This implies that GSD-ST is capable of demodulating randomly combined radio waves, thereby eliminating the effect of interference. To exemplify the potential of GSD-ST, we propose a new radio access scheme, namely non-orthogonal interference-free radio access (No-INFRA). Herein, GSD-ST enables the collision-free reception of uncoordinated access requests. Numerical results show that No-INFRA effectively resolves the colliding access requests when the interference is dominant.

Unmanned aerial vehicles (UAVs) need to "see and be seen" by manned aircraft for their safe operation. For this purpose, using available Automatic Dependent Surveillance-Broadcast (ADS-B) for all UAVs will not only saturate the 1090 MHz spectrum but will require an extra hardware. To mitigate these issues, we propose a ground based sense and avoid (GBSAA) system to enable coexistence of low altitude UAVs and ADS-B enabled flying vehicles (FVs), i.e., manned aircraft, for avoiding collisions. UAVs transmit their location information via a cellular technology to cloud, and a GBSAA base station accesses the aggregated information to send it to the ADS-B enabled FVs via ADS-B technology. We performed analytical and simulation studies to investigate the ADS-B message collision probability for different network parameters such as number of UAVs and ADS-B enabled FVs. Our study shows that for a collision probability of 0.1 with the lowest ADS-B update interval, GBSAA system can support approximately 10 times more UAVs than ADS-B only system. The proposed GBSAA approach provides a tremendous potential to integrate UAVs into airspace in a scalable manner.

This paper presents a scalable scheduler for dynamic TDD systems in ultra-dense indoor deployments applicable to diverse traffic and radio propagation conditions. To minimize signalling for the channel estimation and feedback, the proposed scheduler employs offline BS-to-BS measurements to approximate the real interference for different traffic conditions. Thus, no CSI is required once the network is online. Furthermore, we show that signalling can be further reduced by considering only meaningful interferers above a received power threshold for the traffic information exchange. To perform the scheduling, a function that maps interference into individual BS activation probabilities is also introduced. Results show that the proposed scheme performs reasonably well in high interference situations compared to comparable scalable schedulers, and optimally when interference is low, both in average and 5th percentile sense.

Energy efficiency is of profound importance for prospective 5G wireless networks, especially in sparsely populated rural areas where broadband mobile services should be provided at a reasonable cost. In this paper the impact of beamforming (BF) and cell discontinuous transmission (cell DTX) technologies on the average area power consumption is studied. The required density of base stations for a 5G cellular system in a rural environment is also investigated. For this purpose, we propose a simple rural area model that captures a non-uniform distribution of users and employ the generalized Lloyd algorithm to determine the deployment of base stations. We assume a 5G system operating in mmWave band centered at 28 GHz with the bandwidth of 100 MHz, compared with existing LTE networks at 0.8 GHz with a 20 MHz bandwidth. Simulation results show that for the 5G network the density of base stations needed to provide 50 Mbps for 95% of users at the busy hour will be reduced by 8-9 times with the implementation of BF. It is also observed that BF has a greater effect on the energy saving of 5G networks in rural areas in comparison to the cell DTX.

Dynamic configuring of uplink and downlink switching point in time division duplex (TDD) systems is considered a promising solution to cope with the traffic variations caused by the burstiness of mobile broadband data. However, such dynamic TDD (D-TDD) requires fast inter-cell coordination which may be difficult to implement in ultra-densely deployed networks (UDNs). In order to explore the possibility of designing simplified UDN, we investigate the feasibility of uncoordinated and greedy TDD operation, namely blind D-TDD. It exploits the characteristics of UDN such as low average network utilization and similar transmit power for base stations (BS) and user equipment (UE). To reduce the impact of co-channel interference (CCI), the effect of beamsteering is also evaluated. Our results indicate that blind D-TDD outperforms traditional static TDD (S-TDD) when instantaneous traffic demands for uplink and downlink are highly asymmetric. Also, beamsteering exerts a significant influence on the feasibility of blind D-TDD.

Dense deployment which brings small base stations (BS) closer to mobile devices is considered as a promising solution to the booming traffic demand. Meanwhile, the utilization of new frequency bands and spectrum aggregation techniques provide more options for spectrum choice.Whether to increase BS density or to acquire more spectrum is a key strategic question for mobile operators. In this paper, we investigate the relationship between BS density and spectrum with regard to individual user throughput target. Our work takes into account load-dependent interference model and various traffic demands. Numerical results show that densification is more effective in sparse networks than in already dense networks. In sparse networks, doubling BS density results in almost twofold throughput increase. However, in dense networks where BSs outnumber users, more than 10 times of BS density is needed to double user throughput. Meanwhile, spectrum has a linear relationship with user throughput for a given BS density. The impact of traffic types is also discussed. Even with the same area throughput requirement, different combination of user density and individual traffic amount leads to different needs for BS density and spectrum.

With the increasing number of TV channels and the growing need for on-demand services, the traditional digital terrestrial television is becoming a less attractive way of distributing TV content. As an alternative, we discuss a converged platform in the UHF band for TV and mobile broadband provisioning based on LTE cellular technology and infrastructure, which is here referred to as CellTV. The requirement for CellTV is to provide seamless TV coverage from urban to rural environments and to minimize the spectrum requirement so that the leftover can be used for mobile services. We formulate an optimal spectrum allocation problem for CellTV to distribute different TV channels with different transmission modes. Each TV channel is delivered via either unicast links or the broadcast over single-frequency networks of different modulation orders according to the location-dependent viewing demand and the cellular infrastructure availability. Based on a case study of the Greater Stockholm region, we identify that CellTV only requires a small portion of the UHF band to deliver the TV content in urban areas, thus releasing a significant amount of spectra for mobile broadband services. Meanwhile, the spectrum requirement for CellTV is considerably higher in suburban and rural areas due to the transitions of transmission modes. We further generalize these findings to provide a guiding principle for CellTV deployment in mixed environments and to demonstrate the flexibility advantage of CellTV in adapting to the growing diversity of TV content.

Wireless LANs based on the IEEE 802.11 standard are one of the most commonplace indoor wireless access solutions. As the ever growing demand for data consumption necessitates higher rates and volumes, it is fairly common to observe more and more WLANs being deployed in close proximity to each other. As distances between WLAN installations diminish, the access points (APs) and stations (STAs) in these WLANs create a complex interference environment, which is also compounded by the indoor propagation environment. In this paper, we investigate the impact of two important parameters related to the deployment and operation of densely deployed wireless LANs on the aggregate throughput obtained by all the nodes in these WLANs. The first such operational parameter we investigate is access point and user station association; namely, whether STAs associate with a random "strong" AP or the AP from which they obtain the strongest received power. The second operational parameter we consider is the way in which APs are placed in the indoor environment; namely, whether APs are deployed randomly or in a manner to reduce inter-AP interference. In order to account for the complex node interactions in the MAC layer, which is crucial for accurate performance estimation, we perform packet-level simulations using OPNET. Our results show that the type of node association used in densely deployed WLANs has a critical impact on the aggregate throughput. In comparison, the type of AP deployment used is not nearly as significant; varying from moderate to no impact at all.

We investigate the amount of radio spectrum re- quired for reliable vehicle-to-vehicle (V2V) communication for traffic safety. The basic feature of the traffic safety application is that it uses periodical broadcasts of status messages containing the location and velocity of transmitting vehicles. In our study we consider two dominant technologies for V2V communication, namely IEEE 802.11p and self-organizing time division multiple access (STDMA). We analyze the spectrum demand for a dense highway scenario with a stringent reliability requirement. The results indicate that more than 80 MHz bandwidth is needed to achieve 99% reliability in certain cases. This is in stark contrast to current regulatory decisions that dedicate only 10 MHz bandwidth in 5.9 GHz band for safety purposes in intelligent transportation system (ITS) in Europe and US. Our results suggests that a substantial change would be required in either spectrum allocation or in V2V communication system design to achieve the required traffic safety.

Spectrum combining refers to utilizing multiple types of spectrum authorization options for a wireless network. The approach is considered as an essential ingredient of high-capacity provision in the coming years. This paper presents a techno-economic framework to analyze capacity and cost of different spectrum combining options. We focus on indoor environments where the traffic demand is expected to be extremely demanding. We describe various spectrum options such as licence-exempt, light licensing, and licensed shared access (LSA). Then, we compare various combinations of these options with increasing traffic demand over time. In terms of capacity provisioning, this framework is based on the idea that spectrum combining must be done at the right time, that is when the existing deployment can no longer satisfy capacity demand. For the cost analysis, most relevant cost drivers are included in a cost structure which becomes the backbone of this framework. The proposed framework can help network providers determine the most cost-effective spectrum acquisition strategy which can meet capacity demand in indoor environments.

Most of currently deployed Wi-Fi networks use the IEEE 802.11b/g standard and operate in 2.4 GHz ISMband. As mobile traffic demand rapidly increases, significant Wi-Fi deployment in the still very lightly used 5 GHz band is anticipated. In combination with the recent PHY amendments, e.g., 802.11ac, such Wi-Fi in many settings emerges as a strong competitor to small cellular deployment. In this paper, we aim to quantify what total capacity and which data rates per user can be supported by high-density, the state-of-the-art 5 GHz Wi-Fi deployment. Unlike previous studies, we consider the effect of densification by explicitly modeling the different level of interference among access points for office-type scenarios with various internal wall losses. Although abundant spectrum availability at 5 GHz may compensate for system inefficiency caused by carrier sensing and contention, we find that there is a capacity limit. This capacity limit depends on propagation environments and is especially low in “open” environments or environments with low wall losses. To operate at capacities above this limit, cellular systems with their more advanced interference mitigation techniques are required.

In this paper, we provide a quantitative assessment of the available spectrum for massive indoor broadband secondary access in the 960-1215 MHz band, primarily allocated to the distance measuring equipment (DME) systems. We employ a practical sharing scheme where the secondary users share the DME spectrum via geo-location database and spectrum sensing. Since the DME system performs a safety-of-life functionality, protection from harmful interference becomes extremely critical. A DME channel is considered available in a certain time and location if the secondary users, under the applied sharing scheme, are able to successfully access the channel without violating the primary protection criteria. We analyze the impact of the secondary system parameters and the potential uncertainties in the applied sharing mechanism on the availability in the DME band. Numerical results show that at least 30% of the total DME band (57 MHz out of 190 MHz) can be available for a dense low-power indoor secondary network, even if conservative primary system protection criteria and high levels of uncertainty are considered.

The rapid growth in demand for mobile and nomadic wireless access forces the use of more and more base stations (BSs). In such dense networks, various techniques for multicell interference coordination have been investigated. However, whether or not the interference coordination provides cost benefit compared with a loosely coordinated system is not obvious because the tight coordination at PHY-layer is likely to need an expensive high-speed backbone infrastructure. In this paper, we assess the worthiness of the tight interference coordination, referred to as coordination gain, in various indoor environments. We compare a hypothetical interference-free system as an upper bound with a simple interference-limited system opportunistically avoiding interference. The range of possible coordination gain is examined for various wall losses, path loss exponents, building shapes, and deployment density. Results show that substantial gain can be achieved in dense deployment at open areas with low path loss exponent, e.g., lightly furnished offices partitioned with soft walls. Nevertheless, the coordination gain significantly drops in the presence of marginal wall loss regardless of the other environmental factors.

As the regulation in wireless communications is moving toward a more flexible and efficient way of managing radio spectrum, it is envisaged that multiple small-sized cellular networks owned by different operators, e.g., facility owners or local operators, will operate in close vicinity on shared spectrum. In this environment, the networks may compete for their own utilities in a selfish manner with giving harmful internetwork interference to competitors. In practice, it is not so unusual that each operator has different fairness criteria or quality of service (QoS) strategies by employing distinct objective functions from competitors. Particularly, we in this paper study power control competition between two networks with the sum of rates (SR) and the minimum rate (MR) as their objective functions, respectively. By exploring Nash equilibria, we identify that the MR network benefits from the objective asymmetry thanks to the adaptability of its competitor, i.e., no constraint in the SR objective. On the other hand, the SR network takes disadvantage due to the fairness requirement reflected in the MR objective of its competitor. However, such asymmetry effects in competition becomes negligible with marginal network separation, e.g., indoor deployment in adjacent buildings. Additionally, we identify cooperation potential with the proper choice of a common objective function although the asymmetric objectives are difficult to be aligned.

A self-deployed network is considered to be one of cost-efficient deployment solutions by skipping an expensive network planning process. However, it may result in the serious degradation of capacity or the infeasibility of coverage constraint due to the rise of interference although radio adaptation techniques are employed. Therefore, deployment decision makers, e.g., operators, need to identify when and where the self-deployed network is feasible and economical compared with the planned network. For this, we estimate the average network throughput of the self-deployed network subject to a coverage constraint and compare it with the planned network. Three distinct regions of self-deployment are identified where different deployment strategies are required: infeasible, cost-effective, and uneconomical. We evaluate how the regions alter according to different channel environments and make suggestions for economical deployment.

As the regulation in wireless communications is moving toward a more flexible and efficient way of managing radio spectrum, it is envisaged that multiple small-sized cellular networks owned by different operators will operate in close vicinity on shared spectrum. This brings a new interference environment where a cell is interfered by not only base stations in own network but also those in other networks. These networks may compete for their own utilities in a selfish manner or cooperate in order to minimize the mutual interference. Since a cooperation between the networks requires a business-wise agreement or extra infrastructure cost, the operators have to identify how much they will benefit from the cooperation. In this paper, we compare the effects of competition and cooperation between the cellular networks. The competition and cooperation are modeled as a transmit power control in downlink. It is observed that the cooperation in an average sense gives better network utility. However, as the network size increases, the cooperation gain diminishes significantly. Furthermore, the marginal separation of network deployments, e.g., indoor deployments in adjacent buildings, can notably shrink the cooperation incentive.

This paper presents an analytical model to approximate the probability distribution function of the aggregate interference that a primary user receives from multiple secondary transmitters. In particular, we consider heterogeneity in spatial distribution of secondary users such that there are several sites with densely populated secondary users in the whole area. The concentration of secondary users is modeled as an annulus sector with higher user density, which is termed hot zone. The mathematical framework presented in this paper can readily be adapted to various existing interference models. It is observed that the heterogenous user distribution has a considerable impact on the aggregate interference if the hot zone is near the primary receiver, while hot zones over a certain distance is well approximated by a homogeneous secondary user distribution. The aggregate interference also depends on the shape of the hot zone and the interference threshold imposed on the secondary users.

Coordination of base stations is essential in the mitigation of inter-cell interference in cellular communication systems. One of practical solutions is a cluster-based inter-cell scheduling where base stations in each cluster determine their transmissions in cooperative fashion. In spite of potential performance improvement, the inter-cell scheduling may result in conflict between clusters. However, a dynamic coordination in the cluster level is difficult due to the prohibitive burden of inter-cluster communication. In this paper, we address the coordination of clusters in the downlink of cellular networks. We propose a rule of inter-cluster coordination, namely nominal scheduling order with penalty (NSOP) which does not require communication between the clusters. Dynamic system level simulations are performed to examine the performance of the NSOP in various interference scenarios. It is observed that the proposed NSOP effectively strikes a balance between the inter-cluster interference avoidance and the intra-cluster multi-user diversity by means of a simple penalty factor.

In this paper, we investigate the impact of aggregate interference in a secondary spectrum access system. Particularly, meteorological radar operating in 5.6 GHz band is considered to be a primary user. Secondary users are WLAN devices spreading in a large area which induce aggregate interference to the radar. We develop a mathematical model to derive the probability distribution function (PDF) of the aggregate interference. The derivation considers dynamic frequency selection (DFS) mechanism for the protection of the radar such that the transmission of each WLAN is regulated by an interference threshold. Numerical experiments are performed with various propagation environments and densities of WLAN devices. It is observed that the effect of aggregate interference is severe in a rural environment. The interference threshold for individual WLAN should be much lower than the maximum tolerable interference at the radar. Thus, only a limited number of WLANs can transmit at the same time. On the other hand, adverse effect of the aggregate interference is not shown in an urban environment, where up to 10 WLANs per square kilometer can use the radar spectrum without considering the aggregate interference. The framework discussed in this paper can readily be adapted to assess the aggregate interference for other types of radars.

In this paper we investigate the deployment of LTE indoor femtocells on the frequency band currently used by GSM cellular network. We consider a scenario where the LTE femtocells share GSM uplink spectrum provided that the legacy GSM users are not harmed by interference from the femtocells. Difference in the characteristics of GSM and LTE technologies is exploited to enable the spectrum sharing. The performance of both systems is analyzed mathematically in terms of average SINR. Simulation is employed to support the analysis. Numerical results show that the availability of the spectrum sharing depends on the number of femtocells in each GSM cell and the locations of femtocells.

In this paper we investigate the opportunistic spectrum access in temporal domain where a secondary user shares a radio channel with a primary user during the OFF period of the primary user. We consider practical ON/OFF traffic models whose bursty natures are not properly described by a Markovian assumption. An optimal strategy to determine the transmission power of the secondary user is proposed, which can be adapted to any source traffic model of the primary user. This strategy will maximize the spectrum utilization of the secondary user while keeping interference violations to the primary user below a threshold. Numerical results show that the transmission power of the secondary user depends on the probability distribution of the primary traffic as well as the elapsed time of the OFF period.

Abstract Code division multiple access system with time division duplex (CDMA‐TDD) is a promising solution to cope with traffic asymmetry of downlink (DL) and uplink (UL) in multimedia services. When a rate of asymmetry is different in each cell, CDMA‐TDD system may employ crossed slots, where a timeslot is used for different links in cells. However, it may suffer from base station (BS)‐to‐BS and mobile station (MS)‐to‐MS interference problem. Zone division scheme is an efficient way to tackle the crossed slot interference by dividing a cell into inner and outer zones and restricting communication in crossed slots only to inner zone. In this paper, we propose distributed crossed slot resource allocation with zone division in multi‐cell CDMA‐TDD system. Two conditions for crossed slot resource allocation are defined and the bound on the size of inner zone is analyzed mathematically based on the conditions. Relationship between the capacity of crossed slot and the size of inner zone is also analyzed. Then, numerical results of the mathematical analysis are presented; showing that the proposed crossed slot allocation is effective for traffic asymmetry problem. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract Bluetooth is an open specification for a technology to enable short‐range wireless communications that operate in an ad hoc fashion. Bluetooth uses frequency hopping with a slot length of 625 μs. Each slot corresponds to a packet and multi‐slot packets of three or five slots can be transmitted to enhance the transmission efficiency. However, the use of multi‐slot packet may degrade the transmission performance under high channel error probability. Thus, the length of multi‐slot should be adjusted according to the current channel condition. Segmentation and reassembly (SAR) operation of Bluetooth enables the adjustment of the length of multi‐slot. In this paper, we propose an efficient multi‐slot transmission scheme that adaptively determines the optimal length of slots of a packet according to the channel error probability. We first discuss the throughput of a Bluetooth connection as a function of the length of a multi‐slot and the channel error probability. A decision criteria which gives the optimal length of the multi‐slot is presented under the assumption that the channel error probability is known. For the implementation in the real Bluetooth system, the channel error probability is estimated with the maximum likelihood estimator (MLE). A simple decision rule for the optimal multi‐slot length is developed to maximize the throughput. Simulation experiment shows that the proposed decision rule for the multi‐slot transmission effectively provides the maximum throughput under any type of channel error correlation. Copyright © 2005 John Wiley & Sons, Ltd.

Abstract Future wireless communication systems are expected to provide a broad range of multimedia services that have a significant traffic asymmetry between uplink and downlink. The code division multiple access‐time division duplex (CDMA‐TDD) system is a promising solution to cope with the problem of traffic asymmetry. However, the TDD system is subject to inter‐cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD, uplink and downlink may interfere each other especially when neighboring cells require different rates of traffic load. Thus, the resource allocation among cells is an important issue in TDD. In this paper, the resource allocation in the CDMA‐TDD is formulated as a mixed integer programming (MIP) problem. A dynamic resource allocation algorithm (DRAA) is provided that effectively solves the traffic asymmetry problem. The MIP problem is also solved by a well‐known branch and bound procedure. Both the crossed slot and non‐crossed slot allocation are examined and compared to the DRAA. Computational result shows that proposed DRAA gives a good performance as the traffic asymmetry increases between the uplink and downlink. Copyright © 2003 John Wiley & Sons, Ltd.