Adaptive transmission schemes are a crucial aspect of radio design for future wireless networks. This paper studies the performance of two classes of adaptive transmission schemes in cellular downlink. One class is based on physical layer rateless codes with constant transmit power and the other uses fixed-rate codes in conjunction with power adaptation. Using a simple stochastic geometry model for the cellular downlink, the focus is to compare the adaptivity of fixed-rate codes with power adaptation to that of physical layer rateless codes only. The performance of both the rateless and fixed-rate coded adaptive transmission schemes are compared by evaluating the typical user success probability and rate achievable with the two schemes. Based on both the theoretical analysis and simulation results, it is clearly shown that the fixed-rate codes require power control to maintain good performance, whereas the physical layer rateless codes with constant power can still provide robust performance.

Adaptive transmission schemes are a key part of the radio design for 5G wireless channels. The paper studies the performance of two types of adaptive transmission schemes in cellular downlink. One is based on rateless codes with constant power and the other is fixed-rate codes in conjunction with power adaptation. Using a simple stochastic geometry model for cellular downlink, the focus is to understand the key impact of power adaptation in rateless and fixed- rate coded adaptive transmission. The performance of both rateless and fixed-rate coded adaptive transmission schemes are compared by evaluating the typical user rate and success probability achievable with the two schemes. Based on both theoretical analysis and simulation results, the paper clearly shows that rateless coding simplifies the role of power control in an adaptive transmission scheme.

Rateless codes have been shown to provide robust error correction over a wide range of binary and noisy channels. Using a stochastic geometry model, this paper studies the performance of rateless codes in the cellular downlink and compares it with the performance of fixed-rate codes. For the case of Rayleigh fading, an accurate approximation is proposed for the distribution of the packet transmission time of K -bit information packets using rateless codes. The two types of channel coding schemes are compared by evaluating the typical user and per-user success probability and the rate. Based on both the analytical results and simulations, the paper shows that rateless coding provides a significant throughput gain relative to fixed-rate coding. Moreover, the benefit is not restricted to the typical user but applies to all users in the cellular network.

Rateless codes have been shown to provide robust error correction over wireless channels. Using a stochastic geometry model, this paper studies the performance of cellular downlink with packet transmission based on rateless codes. For the case of Rayleigh fading, a novel and accurate approximation is proposed for the distribution of the packet transmission time of rateless codes. The performance of rateless codes is compared to that of fixed rate codes by evaluating the user rate and success probability achievable with the two channel coding schemes. Based on both the proposed analysis and network simulation, the paper shows that rateless coding provides both coverage and throughput gains relative to fixed rate coding, not only for the typical user but for all users in the cellular network.

Spectrum leasing has been proposed as an effective approach for enabling more flexible spectrum utilization in CRNs. In CRNs, a primary network (PN) which consists of multiple primary users (PUs) can lease part of the licensed spectrum to secondary users (SUs) in exchange for operational benefits. The focus of this study is to investigate how and to what extent the PN allows spectrum leasing in CRNs, considering the QoS requirements of the PN and the secondary network (SN). Correspondingly, we propose two dynamic spectrum leasing strategies, which can improve the QoS performance of SUs while ensuring sufficient remuneration for PUs. In order to dynamically adjust the portion of leased bandwidth, two forms of leasing algorithms, which are based on channel occupancy of the PN and the SN respectively are proposed. Analytical models are developed to characterize system centric performance metrics including capacity, blocking probability, and forced termination probability in both networks. Furthermore, a dynamic pricing scheme for spectrum leasing and utility-based resource allocation is introduced. Finally the performance of dynamic leasing is compared quantitatively with that of static leasing and approaches without leasing. Numerical results obtained from both analysis and simulations show that dynamically adjusted spectrum leasing improves network performance.

Spectrum leasing in cognitive radio networks (CRNs) allows the primary network (PN) to lease a certain fraction of its licensed bandwidth to the secondary network (SN). The motivation for such a concept is to enhance the performance of SNs while improving channel utilization. Meanwhile, the license owners of the channels can also gain benefits through spectrum leasing in terms of either monetary rewards or cooperative communications. In this paper, we propose three dynamic channel access strategies for spectrum leasing in multi-channel CRNs. A common characteristic of all these strategies is that the priority for channel access over the leased spectrum is given to SNs and the unleased spectrum to PNs respectively. The distinction among these three strategies is at the level of opportunistic or exclusive access to leased and unleased spectra by an SN or a PN. The performance of the proposed strategies is evaluated and compared with each other in terms of several system centric metrics including capacity, blocking probability, forced termination probability and channel utilization efficiency.

In this paper, we study the performance of rateless error correction codes in a wireless ad hoc network (WANET). The salient features of a WANET are Rayleigh fading, constant power transmission, pure ALOHA as the channel access protocol, and the nodes being modeled by a homogeneous space-time Poisson point process. For such a WANET, this paper quantifies the rate density (RD) and the dynamic variations of the packet transmission time by deriving an upper bound on the CCDF of the packet transmission time. The performance of rateless codes is compared with two benchmarks, i.e., the ergodic RD (ERD) and the RD of fixed-rate codes. The proposed rateless coding scheme does not require time diversity as each packet is transmitted within a single coherence time. Yet, it is shown that the RD can be up to 76% and 50% of the ERD in noise- and interference-limited regimes, respectively. Thus, the presented network nearly achieves the ERD while requiring significantly shorter delays. This paper shows that a low-complexity Gaussian receiver with a nearest neighbor decoder has almost the performance of an ideal matched receiver. We also show that power control in the form of channel thresholding leads to a 72% gain in the RD relative to a constant power transmission.

In this paper, we do a cost-benefit analysis of multiuser diversity in single antenna broadcast channels. It is well known that the multiuser diversity can be beneficial but there is a significant cost in terms of system resources, bandwidth and power associated with acquiring instantaneous CSI. We work out a cost-benefit analysis of multiuser diversity for 2 types of CSI feedback methods, dedicated feedback and SNR dependent feedback, quantifying how many users should feedback CSI i.e the amount of available multiuser diversity that should be used from a net throughput perspective. Dedicated feedback, in which orthogonal resources are allocated to each user, has significant feedback cost and this limits the amount of available multiuser diversity that can be used. SNR dependent feedback method, in which only users with SNR above a threshold attempt to feedback, has relatively much smaller feedback cost and this allows for all of the available multiuser diversity to be used. Next, we study the effect of single user multiantenna techniques, which reduce the SNR variation, on the number of feedback users. It is seen that a broadcast channel using single user multiantenna techniques should reduce the number of feedback users with the spatial dimension.