# 209

Ingeniero Wireless interview questions shared by candidates

## Top Interview Questions

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DSP Firmware Engineer (Wireless Modem) was asked...6 January 2010

### Swap two numbers without using a temporary variable

x = 10 y = 5 x = x+y // x = 15, y =5 y = x-y // x = 15 , y = 10 x = x-y // x = 15 - 10 = 5 , y = 10 another way, x = x^y y = x^y x = x^y Less

Shift register.

a = a ^ b; b = a ^ b; a = a ^ b;

### You have access to two ports on the RF circuit of a mobile device, one port is at the antenna one at a 50 ohm resistor. Which port will you connect to test the circuit. why describe the advantage and disadvantage of each case.

We connect the testing circuit to the antenna. Resistor is the load

We connect the testing circuit to the antenna. Resistor is the load

### The interviewer focused on the wireless architectures for technical.

Reviewed before my scheduled interview about different wireless architecture.

What do you mean about wireless architecture? Is it the 2G 3G 4G architectures?

### Several questions on statistics, signal processing, communications. Mostly fundamental knowledge, not specific to any standard. Example... need to build a Gaussian random number generator, but the chip only supports uniform distribution. How do I solve this?

Get twelve uniformly distributed random variables and add them, the resulting random variable will be distributed close to Gaussian - says central limit theorem. Less

The answer can be obtained by thinking along the lines of box-muller transformations. Less

### Issues on 2.4GHz for WiFi and other wireless protocols

Check on Channel, CCA, Dynamic Channel Selection algorithms

2.4GHz is a shared band b/w WLAN, Bluetooth and Cellular. Coex and Antenna sharing is a challenge. CCA, Channel selection are part of WLAN protocol. They are effective in 5 GHz band as well. Less

### explain OSI model

I drew the OSI model and explained each layer

In these sorts of interviews you really need to drill down and understand what the interviewer is looking for. A good way to simulate a real interview experience is to do a mock with one of the Huawei Wireless Engineer experts on Prepfully, rated super strongly on TrustPilot... prepfully.com/practice-interviews Less

1,6 and 11

1, 6 &amp; 11

### When you get higher throughput: while going at 5mph and while going at 50 mph? And Why?

high mobility communication is more difficult.

You will get higher a throughput while going at 5mph. Higher speeds indicates that the RF channel conditions such as delay and Doppler spread are changing at fast rate and its a fast fading channel. It is difficult to achieve equalization in such situation. Hence the modulation scheme can be shot down to, say QPSK(2 bits/symbol) from maybe 16QAM(4 bits/symbol) to provide a more robust transmission. This brings down the user throughput. Less