One evening thought: The desire to achieve high through put or data rates is limited by multi-path nature of wireless channels. Reduced symbol time enables increased data rates but multi-path nature of the channel results in ISI (Inter symbol interference). ISI occurs when the symbol time is less than delay spread of the channel. So, if … Continue reading CDMA RAKE

# Relation between BER and PER

Its interesting to know that it depends on size of packet(N) A packet is error if one or more number of bits are errors. P(Ne>=1) = 1-P(Ne=0) Pb = Probability of bit error (Pb+1-Pb)^N = Nc0*(Pb)^N + Nc1*(Pb)^(N-1)*(1-Pb)+ .....+ NcN*(1-Pb)^N P(Ne=0) = (1-Pb)^N P(Ne>=1) = 1 - (1-Pb)^N For suppose in Bluetooth, a BER constraint … Continue reading Relation between BER and PER

# Poison puzzle

One among 100 bottles of water is poisoned. What is the minimum number of people required to find the poisoned bottle. [It takes an hour for the poison to effect on the person, and you have only one hour to find the poised bottle] mail me to know the answer...

# Convolution Interleaver

The below figure is being referred in many links on the web to explain convolution interleaver. Should n't the output be like ....X0,X-3,X-6,X-9,X4,X1,X-2,X-5.... instead of ...X0,X-3,X-6,X-9,X4,X-2,X-5,... as shown in figure. Many of the below links refer to this same figure: [1]https://wiki.cse.buffalo.edu/cse545/content/burst-error-correcting-codes [2 https://en.wikipedia.org/wiki/Burst_error-correcting_code#Convolutional_interleaver

# BB to PB to BB conversion

In Heterodyne receiver, RF frequency is converted to IF frequency and then IF is converted to Base band. (Two mixers?) In monodyne receiver, RF frequency is directly converted to Base Band. (One mixer).

# Dynamic range of ADC

Dynamic Range (DR) describes the range of input signal levels that can be reliably measured simultaneously, in particular the ability to accurately measure small signals in the presence of the large signals. It depends on the number of bits the ADC uses to represent the data. suppose if resolution is 16-bit then DR = 20*log10(65536) … Continue reading Dynamic range of ADC

# Finite State Machine (FSM)

There are two kinds of FSM Moore FSM: Output depends on only current state Mealy FSM: Output depends on current state as well as current input. Encoding styles Binary encoding: 000,001,010,011... Gray encoding: 000,010,011.. one hot: 0001,0010,0100,1000 one cold: 1110,1101,1011,0111 Mostly we end up using mealy FSM (More practical). Moore FSM may need more states … Continue reading Finite State Machine (FSM)

# Linear dependent vectors

What is the condition for three vectors (suppose u,v & w) to be linearly dependent. suppose u = [u1 u2 u3]; v = [v1 v2 v3]; w = [w1;w2;w3]; matrix (M) = [u1 v1 w1; u2 v2 w2; u3 v3 w3] X = [x;y;z] MX = 0; Homogeneous equations. If one vector can be expressed … Continue reading Linear dependent vectors

# Convolution Encoder in C

Consider a rate half (1/2) convolution encoder with generator polynomials defined by G1 = [1,1,1] & G2 = [1,0,1] and constraint length as 3. #define G1 7 #define G2 5 bool GetParity (int N) { bool Parity = 0; while(N) { parity = !parity; N = N&(N-1); } return parity; } int main () { int … Continue reading Convolution Encoder in C

# Void & NULL pointers

In one line, It can said that, they are completely different concepts and should not be compared. Void pointer is a generic pointer and is used when there is no idea about the type of pointer that we are expecting. For example, we use malloc or calloc to dynamically allocate some bytes of memory and … Continue reading Void & NULL pointers