WiMAX – Page 3

September 13, 2011November 15, 2011LTE, Network Planning, WiMAX

Propagation and In-Building Penetration at 700MHz

It is quite well known that wireless signals travel further at lower frequencies. This phenomenon has become particularly important in the context of LTE where a frequency band has been allocated at 700MHz. We would like to quantify the benefits that can be achieved by using this frequency band. Firstly we find the received signal power at 728 MHz (lowest downlink frequency) and at 3600 MHz (highest downlink frequency) in a free space line of sight channel. The transmit power is set to 1 W and omnidirectional antennas are considered at the transmitter and receiver. The received power for these […]

September 9, 2011May 31, 20225G, BER Performance, LTE, Modulation, WiMAX

BER of 64-QAM OFDM in Frequency Selective Fading-II

It is observed that the BER performance of 64-QAM OFDM in the time-varying frequency-selective channel is quite similar to that in the static frequency-selective channel with complex filter taps. It must be noted that with 64-QAM the goal is to achieve higher bit rate, error rates can be improved using antenna diversity and channel coding schemes.

September 3, 2011May 31, 20225G, BER Performance, LTE, Modulation, WiMAX

BER of 64-QAM OFDM in Frequency Selective Fading

The real benefits of OFDM become apparent in a frequency selective channel. The introduction of the cyclic prefix (guard period) allows us to remove the Intersymbol Interference (ISI) in the time domain and frequency domain equalization allows us to overcome the channel variations in the frequency domain.

September 2, 2011May 31, 20225G, BER Performance, LTE, Modulation, WiMAX

BER of 64-QAM OFDM in AWGN

64-QAM is an important component of 4G/5G Air Interface that promises higher data rates and spectral efficiencies. Combined with OFDM and MIMO it successfully combats the detrimental effects of the wireless channels and provides data rates in excess of 100Mbps (peak data rate). Here, we discuss a simple example of 64-QAM modulation with OFDM in an AWGN channel. We assume a bandwidth of 1.25MHz which corresponds to an FFT size of 128.

September 1, 2011May 31, 20225G, BER Performance, LTE, Modulation, WiMAX

Bit Error Rate of 64-QAM in AWGN

64-QAM is an important modulation scheme being used in WiMAX and LTE. It allows for transmission of 6 bits symbol which results in higher bit rate and spectral efficiency. The calculation of bit error rate of 64-QAM is a bit tricky as there are many different formulas available with varying degrees of accuracy. Here, we first calculate the bit error rate (BER) of 64-QAM using a simulation and then compare it to the theoretical curve for 64-QAM. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % FUNCTION TO CALCULATE 64-QAM BER USING SIMULATION % n_bits: Input, number of bits % EbNodB: Input, energy per bit to noise […]

August 31, 2011May 31, 20225G, BER Performance, LTE, Modulation, WiMAX

OFDM Modulation and Demodulation (AWGN) – II

We have previously looked at a simple OFDM modulation and demodulation scheme. We saw that the BER performance of OFDM in AWGN was the same as the BER performance of the underlying modulation scheme (QPSK in this case). We will now continuously improve upon our basic simulation to get a more realistic picture. In this regard we introduce the cyclic prefix which is used in OFDM to overcome Intersymbol Interference. The duration of the cyclic prefix is 0.8usec (16 samples at 20MHz) resulting in a symbol duration of 4usec (IEEE 802.11a). Given below is the code for OFDM modulation and demodulation […]

August 30, 2011May 31, 20225G, BER Performance, LTE, Modulation, WiMAX

OFDM Modulation and Demodulation (AWGN)

OFDM modulation works on the principle of converting a serial symbol stream to a parallel symbol stream with each symbol from the parallel set modulating a seperate carrier. The spacing between the carriers is 1/T where T is the duration of the OFDM symbols (without cyclic prefix). This guarantees orthogonality of the carriers i.e. there is no interference between carriers. The addition of orthogonal carriers modulated by parallel symbol streams is equivalent to taking the IFFT of the parallel symbol set. At the receiver the inverse operation of FFT is performed and the parallel symbol streams are converted to serial symbol streams. The main advantage of this scheme is that one […]

May 30, 2011August 23, 2011WiFi, WiMAX

Laptop Orientation and Data Rate

I live in a basement and do not get very strong WiMAX signals so I have placed my WiFi router outside my home. Now the distance between my laptop (Toshiba Satellite L645) and the WiFi router is larger than I would like it to be. I noticed that the download speed that I get is highly dependent on the orientation of my laptop. So here are the results of download speeds for various antenna orientations. So I am assuming that there is some sort of surface antenna on this laptop that works well in certain directions but does not work […]