北邮温向明组推免笔试题

PhD candidate quiz (You should answer the questions by English, and write down your answers after the question in bold red text)Warm-up1.Connect the 12 dots below with 5 straight lines, without lifting the pen from the paper,finishing where you started2.Flipping a fair coin, where obverse denotes success and reverse denotes failure. Obviously,the probability of success is 0.5. Independent trials are performed until there are 2consec utive successes. Let Χ denote the number of trials. The mean number of trialsE[Χ]= 4Wireless communications3.Consider a receiver with the following characteristics: Bandwidth: 7.68MHz, noise figure7dB, receive antenna gain: 2dB. Further a transmitter with a transmit power of 15dBm and an antenna gain of 10dB. If the path loss is 120 dB, what is the signal to noise ratio (SNR) at the receiver?B=7.68MHz=69dBHzP n=-174+69=-105dBmSNR=15+10+2-120-(-105)-7=5dB4.Which of the following statements about MIMO communication systems is true?A.MIMO can increase capacity (over a SISO system) by the factorR=min(Ntx,Nrx), where Ntx and Nrx is the number of transmit and receiveantennasB.MIMO can increase diversity of the system with a maximum diversity gain ofd=Ntx*NrxC. A + B at the same timeD.MIMO systems require the elements of the channel to be i.i.d.E.Bonus question: what is the relationship between R and d?5.What are the benefits of the cyclic prefix in OFDM?A.It eliminates inter-symbol interference coming from the multipath propagationB.It maintains orthogonality between subcarriersC.It makes OFDM scalableD.It increases the spectral efficiency4G/5G6.What coding scheme is used for the PDSCH and PUSCH in LTE?A.Rate 1/3 tail-biting convolutional codeB.Rate 1/3 turbo codeC.Variable-rate block codeD.Rate 1/3 repetition code7.In LTE, what is the benefit of PAPR reduction in the uplink?A.Improved uplink coverageB.Lower UE power consumptionC.Reduced equalizer complexityD.All of the above8.The size of a resource block in LTE is 180kHz in frequency and 0.5ms in time. Assumingthat the channel stays approximately constant over this period of time and frequency, whatis the maximum supported Doppler shift D and the maximum supported delay T of thechannel?T=D=WLAN9.Which of the following versions of IEEE 802.11 protocol can run in the 2.4GHz band andthe 5GHz band?A. IEEE 802.11aB. IEEE 802.11gC. IEEE 802.11nD. IEEE 802.11ac10.How can you configure Wi-Fi network and what are Wi-Fi Protocols?WiFi is a technology for wireless local area networking with devices based on theIEEE 802.11 standards. Wi-Fi is a trademark of the Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that successfully completeinteroperability certification testing.Devices that can use Wi-Fi technology include personal computers, video-gameconsoles, smartphones, digital cameras, tablet computers, digital audio players and modern printers. Wi-Fi compatible devices can connect to the Internet via a WLAN and a wireless access point. Such an access point (or hotspot) has a range of about 20 meters (66 feet) indoors and a greater range outdoors. Hotspot coverage can be assmall as a single room with walls that block radio waves, or as large as many square kilometres achieved by using multiple overlapping access points.Depiction of a device sending information wirelessly to another device, bothconnected to the local network, in order to print a documentWi-Fi most commonly uses the 2.4 gigahertz (12 cm) UHF and 5 gigahertz (6 cm)SHF ISM radio bands. Having no physical connections, it is more vulnerable toattack than wired connections, such as Ethernet.11.What are the different WiFi generations and also explain any one?Frequency, modulation and Stream data rate are diffrerent.The 802.11b standard has a maximum raw data rate of 11 Mbit/s, and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulationtechnique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with simultaneous substantialprice reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.Devices using 802.11b experience interference from other products operating in the2.4 GHz band. Devices operating in the 2.4 GHz range include microwave ovens,Bluetooth devices, baby monitors, cordless telephones, and some amateur radioequipment.Internet of Things12.What kind of wireless technology can be applied to IoT?ZigBee, wifi,Bluetooth13.What’s the difference between IoT and mobile Internet?The mobile Web refers to browser-based Internet services accessed from handheld mobile devices, such as smartphones or feature phones, through a mobile or otherwireless network.The IoT is the inter-networking of physical devices, vehicles, buildings, and otheritems embedded with electronics, software, sensors, actuators, and networkconnectivity which enable these objects to collect and exchange data.pared with the traditional user equipment, show your opinions on the communicationcharacteristics of devices in the IoTlow power consumption, Strong stability,low speed.15.What are the main issues for devices in the IoT? Can you give some solutions for them?Complexity and unclear value propositions, Privacy and security concerns.16.Which of the following statements are not correct about energy Internet?A. There are more distributed clean energy generators and more intelligent devices,such as smart meters, in energy Internet.B. Large amounts of data will be generated and big data technologies will be greatlyneeded.C. The volatility of clean energy will be relieved with its large-scale deployment.D. MTC、NB-IoT and Lora technologies will be important for the access ofdistributed generators.C Programming17.Which of the following statements are correct about the function?long fun(int num){int i;long f=1;for(i=1; i<=num; i++)f = f * i;return f;}E.The function calculates the value of 1 raised to power num.F.The function calculates the square root of an integerG.The function calculates the factorial value of an integerH.None of above18.Which of the following statements are correct about an array?A.The array int num[26]; can store 26 elements.B.The expression num[1] designates the very first element in the array.C.It is necessary to initialize the array at the time of declaration.D.The declaration num[SIZE] is allowed if SIZE is a macro.19.Point out the correct statement which correctly allocates memory dynamically for 2Darray following program?#include<stdio.h>#include<stdlib.h>int main(){int *p, i, j;/* Add statement here */for(i=0; i<3; i++){for(j=0; j<4; j++){p[i*4+j] = i;printf("%d", p[i*4+j]);}}return 0;}1.p = (int*) malloc(3, 4);2.p = (int*) malloc(3*sizeof(int));3.p = malloc(3*4*sizeof(int));4.p = (int*) malloc(3*4*sizeof(int));20.Let a and b be fixed point numbers in Q15 format. Which of the following statementscomputes the product a*b in Q15 format#include<stdio.h>#include<stdlib.h>int main(){short i=0x7FFF, j=0x2000;short ret;/* Add statement here */return ret;}A.ret = a*b;B.ret = (short) ((float) a * (float) b);C.ret = (short) (((int) a * (int) b) >> 15);D.ret = (a >> 15) * (b>>15);E.Bonus question: what is the correct value of ret?21.Write a function that computes the inner product of two real-valued floating point vectorsof size N:float inner_product(float* a, float*b, int N){/* your code here */int i;float sum=0;for(i=0;i<N;i++){sum=sum+a[i]*b[i];}return sum;}22.Let the compiler be 32-bit mode in C99 standard. Which is the correct result of sum1 andsum2?#include <stdio.h>#include <stdlib.h>int sumarray(int a[]){int result = 0;for(unsigned int i=0;i<sizeof(a);i++)result+=a[i];return result;}int main(){int array1[] = {6,5,4,3,2,1};int sum1 = 0;for(unsigned int i=0;i<sizeof(array1)/sizeof(int);i++)sum1+=array1[i];int sum2 = sumarray(array1);printf("sum1 = %d, sum2 = %d.\n",sum1,sum2);return 1;}A. sum1 = 21, sum2 = 6;B. sum1 = 21, sum2 = 21;C. sum1 = 21, sum2 = 18;D. sum1 = 6, sum2 = 6;E. Bonus question: What will happen if we use a 64-bit complier?To finish23.Why do you want to do a Master or PhD?I want to study wireless communications, FPGA,Embedded system or other thingscombined of software and hardware.。