The Cost of Mitigating Power Law Delay in Random Access Networks

Abstract

Abstract-Exponential backoff (EB) is a widely adopted collision resolution mechanism in many popular random-access networks including Ethernet and wireless LAN (WLAN). The prominence of EB is primarily attributed to its asymptotic throughput stability, which ensures a non-zero throughput even when the number of users in the network goes to infinity. Recent studies, however, show that EB is fundamentally unsuitable for applications that are sensitive to large delay and delay jitters, as it induces divergent second-and higher-order moments of medium access delay. Essentially, the medium access delay follows a power law distribution, a subclass of heavy-tailed distribution. To understand and alleviate the issue, this paper systematically analyzes the tail delay distribution of general backoff functions, with EB being a special case. In particular, we establish a tradeoff between the tail decaying rate of medium access delay distribution and the stability of throughput. To be more specific, convergent delay moments are attainable only when the backoff functions g(k) grows slower than exponential functions, i.e., when g(k) ∈ o r k for all r > 1. On the other hand, non-zero asymptotic throughput is attainable only when backoff functions grow at least as fast as an exponential function, i.e., g(k) ∈ Ω r k for some r > 1. This implies that bounded delay moments and stable throughput cannot be achieved at the same time. For practical implementation, we show that polynomial backoff (PB), where g(k) is a polynomial that grows slower than exponential functions, obtains finite delay moments and good throughput performance at the same time within a practical range of user population. This makes PB a better alternative than EB for multimedia applications with stringent delay requirements.Index Terms-Medium access control, backoff algorithms, wireless LAN (WLAN), power law delay.

Distributed scheduling in wireless powered communication network: Protocol design and performance analysis

“…Without loss of generality, we assume 1 3 N WDs are type-I and the rest 2 3 N WDs are type-II, and p t = 1 N . For brevity, we only present the results for the probability of a WET slot (P ene in (12)) and that of a successful transmission slot (P suc in (13)). We can see that the simulation and analysis match well, which validates our proposed analytical method.…”

“…Therefore, the N WDs have the same average data rate ψ/N . From (12), if some WD n has very high probability of energy outage, i.e., large w 0 n , the data rates of all the WDs can be very low. Therefore, our proposed method should be applied to a network with limited WET range, e.g., the maximum WD-to-HAP distance is less than 10 meters to ensure that all WDs can be effectively charged by the HAP.…”

“…In this case, distributed scheduling of WET and WIT is of high practical interests. Although distributed wireless charging control and data transmissions have been well investigated separately (e.g., [9]- [12]), there are only few studies integrating them in the design of WPCN. For instance, [13] proposes an energyadaptive CSMA-type MAC (medium access control) method, where the access probability of a WD decreases with its energy harvesting rate.…”

Analysis of Queuing Delay and Medium Access Distribution over Wireless Multihop PANs

“…This is attributed to the fact that increasing the variations of the interarrival and service times of packets reduces the contention to access the channel which in turn reduces the probability of lost packets. It is worth noting that this behaviour constitutes one of the key reasons behind the wide applicability of CSMA-CA protocol, as the throughput of CSMA-CA protocols does not approach zero even if the traffic intensity or number of nodes are high [47]. However, the downside of this behaviour is that increasing the variations of inter-arrival and service time distributions can underutilise the network resource especially in multi-hop networks.…”