3rd Int'l Conf. on Recent Advances in Information Technology I RAIT-2016I
A Modified NCO based LSPF-DPLL Phase Resolver for Wireless Communication -Comparative Analysis with LSPF-DPLL
I
Sabyasachi Bhattacharyya
2Aradhana Misra Dept. of Electronics and Communication Engineering Gauhati University Institute of Science and Technology Guwahati, India
[email protected] 2
[email protected]
Abstract-With
rapid
advancements
in
communication
technologies, 5G is already in the reckoning. Communication systems that can serve low error rates at minimum delay are the need of the hour. DPLL based receivers are popular in modern day communication setups. Such standalone receivers based on Least Square Polynomial Fitting (LSPF) and Zero Crossing (ZC) techniques have been recently proposed. These systems exhibit satisfactory error performance at the cost of degraded time performance involving intensive computations.
A Modified NCO based LSPF-DPLL Phase Resolver with superior error and time performance as compared to existing LSPF-DPLL is presented here.
Keywords- time efficieny; roots; fitting; fading; phase resolver I.
INTRODUCTION
Digital Phase Locked Loops (DPLLs) are the digital domain version of the Phase Locked Loops (PLLs) with a digital Phase-Frequency Detector (PFD) [1][2]. DPLLs exhibit versatility serving a number of purposes in communication setups like performing carrier recovery in non-coherent systems where the channel information is not known to the receiver [2], symbol recovery in coherent setups for known channel [3], clock distribution into different sub-systems using PLL divider besides maintaining time synchronization in such systems [2]. This leads to wide deployment of DPLL systems. A Zero Crossing Digital Phase Locked Loop (ZC DPLL) is proposed in [1] exhibiting a linearized phase detector response, faster locking, less steady state phase error and wider lock-in range. Another contemporary design of a ZC-DPLL has been proposed in [4] for high Doppler environments. It introduces a hyperbolic non-linearity and a sigma-delta unit for better adaption of the loop filter providing superior time jitter and lock-in range performance. The LSPF-DPLL proposed in [2] utilizes a computationally intensive Left/Right (LlR) shift algorithm based Numerically Controlled Oscillator (NCO) and an LSPF based PFD to achieve satisfactory error rates but leads to degraded time performance due to intensive LIR shift algorithm in [2]. A similar computationally intensive LIR
978-1-4799-8579-1/161$31.00 ©2016 IEEE
3Kandarpa Kumar Sarma Dept. of Electronics and Communication Teclmology Gauhati University Guwahati, India
[email protected]
Shift algorithm based Digitally Controlled Oscillator (DCO) is incorporated in the ZC-DPLL system proposed for Rayleigh faded channels in [3]. It shows good error performance but the intensive LIR shifting leads to degraded time performance of the system. Recent DPLL designs proposed in [1][4] emphasize on time efficient recovery of symbols under degraded wireless environments. Another category of DPLL design however focuses on achieving significantly lower BER levels involving computationally intensive processes that lead to degraded time performance. The LSPF-DPLL system in [2] and the ZC-DPLL system in [3] involve complex LIR shift algorithms in their NCO and DCO units respectively leading to poor time performance. A modified NCO based LSPF DPLL phase resolver is proposed here. The modified NCO uses a look-up table consisting of dibits and phases transmitted available at the receiver to provide accurate phase match avoiding the time consuming LIR shift algorithm in [2][3] exhibiting better error and time performance as compared to LSPF-DPLL in [2]. The remaining portion of this paper is structured as follows. In Section II, the system model for the modified NCO based LSPF-DPLL Phase Resolver is discussed emphasizing on its different sub-units and their operations, related mathematical equations and simulation parameters. The modifications made in proposed Phase Resolving NCO are also discussed in details. Section ill shows results obtained for the proposed system and a comparative analysis of the system with the LSPF-DPLL system proposed in [3]. In Section IV, the system advantages and limitations are discussed and finally the discussion is summarized in Section V. II. SYSTEM MODEL The LSPF-DPLL phase resolver design presented here is subjected to degraded QPSK modulated symbols under Rayleigh and Rician faded wireless environments aided by Additive White Gaussian Noise (AWGN).
3rd Int'l Conf. on Recent Advances in Information Technology I RAIT-2016I
retrieves transmitted bit streams over Rayleigh and Rician Faded Wireless Channels aided by A WGN noise.
A. System Architecture:
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