Novel Windowing Scheme for Cognitive OFDM Systems

2018 2nd International Conference on Recent Advances in Signal Processing, Telecommunications &Amp; Computing (SigTelCom)

Hoang

et al. 2018

Orthogonal frequency division multiplexing (OFDM) has been widely adopted for modern wireless standards and become a key enabling technology for cognitive radios. However, one of its main drawbacks is significant spectral leakage due to the accumulation of multiple sinc-shaped subcarriers. In this paper, we present a novel pulse shaping scheme for efficient spectral leakage suppression in OFDM based physical layer of IEEE 802.11af standard. With conventional pulse shaping filters such as a raised-cosine filter, vestigial symmetry can be used to reduce spectral leakage very effectively. However, these pulse shaping filters require long guard interval, i.e., cyclic prefix in an OFDM system, to avoid inter-symbol interference (ISI), resulting in a loss of spectral efficiency. The proposed pulse shaping method based on asymmetric pulse shaping achieves better spectral leakage suppression and decreases ISI caused by filtering as compared to conventional pulse shaping filters. 1

“…The second, denoted as 𝑝 2 , is based on the characteristics of function with vestigial symmetry as derived in [13]. The function of the vestigial symmetry window is given as…”

Section: A Pulse Shapingmentioning

confidence: 99%

An efficient spectral leakage filtering for IEEE 802.11af in TV white space

Nguyen

2018 2nd International Conference on Recent Advances in Signal Processing, Telecommunications &Amp; Computing (SigTelCom)

Hoang

et al. 2018

“…The third, denoted p 3 , is based on the characteristics of functions with vestigial symmetry as derived by Castanheira and Gameiro [29]:…”

Section: Pulse Shapingmentioning

confidence: 99%

Spectrally efficient emission mask shaping for OFDM cognitive radios

Digital Signal Processing

Fahmy

McLoughlin

2016

Orthogonal Frequency Division Multiplexing has been widely adopted in recent years due to its inherent spectral efficiency and robustness to impulsive noise and fading. For cognitive radio applications in particular, it can enable flexible and agile spectrum allocation, yet suffers from spectral leakage in the form of large side lobes, leading to inter-channel interference, unless mitigated carefully. Hence, recent OFDM-based standards such as 802.11p for vehicular communication and 802.11af for TV whitespace impose strict spectrum emission mask limits to combat adjacent channel interference. Stricter masks allow channels to operate closer together, improving spectral efficiency at the cost of implementation difficulty. Meeting the strict limits is a significant challenge for implementing both 802.11p and 802.11af, yet remains an important requirement for enabling cost-effective systems. This paper proposes a novel method that embeds baseband filtering within a cognitive radio architecture to meet the specification for the most stringent 802.11p and 802.11af masks, while allowing ten 802.11af sub-carriers to occupy a single basic channel without violating SEM specifications. The proposed method, performed at baseband, relaxes otherwise strict RF filter requirements, allowing the RF subsystem to be implemented using much less stringent 802.11a designs, allowing cost reductions.

“…The second is based on a raised cosine function proposed by Bala et al [13]. The last is based on the characteristics of functions with vestigial symmetry presented by Castanheira and Gameiro [14]. The three functions are rewritten in discrete form in Equations (3), (4), (5), respectively.…”

Section: Using Pulse Shaping For 80211pmentioning

confidence: 99%

Shaping Spectral Leakage for IEEE 802.11p Vehicular Communications

2014 IEEE 79th Vehicular Technology Conference (VTC Spring)

McLoughlin

Fahmy

2014

Abstract-IEEE 802.11p is a recently defined standard for the physical (PHY) and medium access control (MAC) layers for Dedicated Short-Range Communications. Four Spectrum Emission Masks (SEMs) are specified in 802.11p that are much more stringent than those for current 802.11 systems. In addition, the guard interval in 802.11p has been lengthened by reducing the bandwidth to support vehicular communication (VC) channels, and this results in a narrowing of the frequency guard. This raises a significant challenge for filtering the spectrum of 802.11p signals to meet the specifications of the SEMs. We investigate state of the art pulse shaping and filtering techniques for 802.11p, before proposing a new method of shaping the 802.11p spectral leakage to meet the most stringent, class D, SEM specification. The proposed method, performed at baseband to relax the strict constraints of the radio frequency (RF) front-end, allows 802.11p systems to be implemented using commercial off-theshelf (COTS) 802.11a RF hardware, resulting in reduced total system cost.