S. Ghavami, B. Abolhassani,
Volume 9, Issue 1 (3-2013)
Abstract
In the down link scenario of code division multiple access (CDMA) systems, multi user detectors (MUDs) such as linear de-correlating detector (LDDs) provide satisfactory symbol error rates (SERs) at the expense of much increased complexity, they require all active users’ spreading sequences, which is impractical from privacy point of view. To overcome this impracticality, a simple matched filter receiver is considered in this paper, which requires no knowledge of co-users’ spreading sequences. However, this simple receiver degrades the SER due to multiple access interference (MAI). To overcome this SER degradation, a zero force (ZF) pre-coder is employed in the transmitter traditionally. Moreover, a composite of CDMA signals has a large peak to average power ratio (PAPR), which causes nonlinear distortion (NLD) at the output of the base station high power amplifier (HPA). This also results in degrading the SER. We analyze the down link scenario of CDMA system to derive an equation for the SER of system with ZF-pre-coder plus HPA in the transmitter and matched filter in the receiver over two cases: additive white Gaussian noise (AWGN) and AWGN plus flat fading channels. Theoretical analysis and numerical results show that the ZF pre-coder increases the total degradation of the link significantly compared with that of the LDD. So, as a solution, rather than using ZF pre-coder, we propose a new method which is called extended joint channel estimation method, it is based on joint estimation of channel gains and LDD operator by the mobile station (MS). In that base station (BS) transmits the row k of LDD operator to the MS k. Simulation results show that the SER of this new proposed method is matched to that of LDD in AWGN channel when the number of pilot symbol repetition is equal to 8. Moreover, this method has the two added advantages of no need for providing the spreading sequences of all co-users and meeting a satisfactory total degradation. Furthermore, our analysis shows that loss in spectral efficiency due to transmitting the pilot symbols in the proposed method is negligible for the practical values of traffic variations.
S. Juneja, R. Sharma,
Volume 15, Issue 4 (12-2019)
Abstract
Design of Global Positioning System (GPS) receiver with a low noise amplifier (LNA) in the front end remains a major design requirement for the success of modern day navigation and communication system. Any LNA is expected to meet the requirements like its ability to add the least amount of noise while providing sufficient gain, perfect input and output matching, and high linearity. However, most of the reported designs of LNAs present the need for striking a trade-off between these design parameters in order to obtain the desired performance for a particular RF receiver. This paper presents high gain (21dB), high input matched (-29dB), high reverse isolation (-41dB) and low noise figure (< 2dB) narrowband LNA for extremely low power level GPS L1 band signals broadcasting at 1.57GHz with a channel bandwidth of 10MHz. Inductive source degeneration topology is employed for the design and all the matching inductors in the circuit are used with fixed quality factor (Q) to model the losses for better tuning and matching. The design is carried out on Cadence Virtuoso Tool version IC6.1.6 and Spectre version MMSIM13.1 at 0.18µm technology node using a generic process development kit. Detailed mathematical analysis of the design is done and all the DC parameters like values of transconductance, gate source capacitance, drain source voltage, drain current, etc. are reported. Graphical analysis using Smith chart is carried out to present the results and to bring forth the trade-offs involved in the design. LNA draws 5mA current from 1.2V supply voltage and offers good linearity that is sufficient for GPS application and is measured by input intercept point 3 (IIP3 < ‑4dBm).
