UNIT I

PHYSICAL AND WIRELESS MAC LAYER ALTERNATIVES

 PART – A (2 Marks)

1. Name five design consideration in selecting a modulation scheme for a wireless networks.

i. Bandwidth efficiency, ii. Power efficiency, iii. Out of band radiation, iv. Resistance to multi path, v. Constant envelope modulation.

2. Why is out of band of radiation an important issue in designing modulation scheme?

Because, out of band radiation is the source of interference.

3. Why is PPM used with IR communication instead of PAM?

In PAM as the signal is through amplitude, the wireless channels suffer amplitude fluctuations because of fading and near far problems. So PPM is used in wireless communication instead of PAM.

4. Name four space diversity techniques.

i. Multiple antennas, ii. Polarization diversity, iii Sectored antennas, iv. Adaptive angle diversity.

5. What are the advantages of high efficiency voice band modems?

The advantages of high efficiency voice band modems are,

            i.          It provides good bandwidth efficiency.

1. It can reduce the connect time

6. Define DFE.

 DFE -  Decision Feed back Equalizer. This Equalizer is used  for multipath fading channels.

7. Define ACI.

ACI means adjacent carrier interference. It is the interference caused by a transmitting channel to its above and below channels. It is because of out of band radiation.

8. What are the types of diversity?

i. Time Diversity, ii. Frequency Diversity, iii. Space Diversity

9. In an OFDM modem with 48 channels, each channel uses 16 QAM modulations. if the overall transmission rate is 10 Mbps. What is the symbol transmission rate per channel?

The symbol transmission rate per channel= (10/4)/48 = 52.083 KHz.

 10. What are the sectored antennas? How they are useful in combating multipath?

A sectored antenna has several sectors each selecting only the signal arriving in their field of view. A sectored antenna reduces the interference from other users operating in the same band because it restricts the spatial angle of the arriving interference signals.

11. What are the popular access schemes for data networks? Classify them.

i. Different ALOHA Techniques, ii. CSMA Techniques, iii CSMA/CD, iv.CSMA/CA,

v. RTS/CTS

12. What is the difference between the access technique of IEEE802.3 and IEEE802.11?

IEEE802.3 uses CSMA/CD but IEEE802.11 uses CSMA/CA protocol. Because when CSMA/CD is used in IEEE802.11, collision cannot be identified. 

13. What is the difference between performance evaluations of voice oriented fixed assignment and data oriented random access?

In voice oriented fixed assignment network, circuit switching is used and delay cannot be tolerated, but packet loss can be accepted. In data oriented random

access networks, packet switching is used. Here delay can be tolerated but packet loss cannot be tolerated. As the requirements of data and voice networks differ their performance evaluations also differ.

14. What is the difficulty of implementing CSMA /CD in a wireless environment?

When we use CSMA/CD in wireless applications collision cannot be detected because of multipath effect and near far problem.

15. Explain about CSMA.

CSMA - it is also called as Listen Before Talk. This technique reduces collision considerably compared to ALOHA, because it senses the availability of the channel first and then transmits.

16. Explain about hidden terminal problem.

In wireless networks, when two terminals are not within the radio range to each other then they cannot transmit directly. This is called hidden terminal problem.

17. Explain about capture effect.

In FM reception, when we have more than one signal the stronger signal is selected that is called capture effect.

18. Write down the formula for N idle.

N idle = N – ρ (1- B(N, ρ))

 19. Define: a. persistent, b. non persistent, c. 1-persistent, d. p-persistent

After sensing a busy channel, if the terminal continues sensing the channel until the channel becomes free the protocol is called Persistent CSMA.

If After sensing the channel, the terminal attempts another sensing only after a random waiting period,

the protocol  is called Non Persistent CSMA .

In Persistent operation, after the channel becomes free, if the terminal transmits immediately then the protocol is called 1- Persistent.

In Persistent operation, if it runs a random number generator and based on outcome transmit its packet with a probability p, it is called p- Persistent.

20. Difference between ALOHA and slotted ALOHA.

ALOHA                                                         Slotted ALOHA

1.It is very simple. No Synchronization          Synchronization between time slots.

2.Throughput is 18%                                       Throughput is 36%

21. Explain about space diversity.

In a fading multipath channel, the received signal at the antenna of a receiver is composed of a number of signals arriving through different paths from different spatial angles. Spatial diversity is provided by multiple antennas.

UNIT II

WIRELESS NETWORK PLANNING AND OPERATION

 

PART –A (2 Marks)

1. Name any three advantages of an infrastructure topology over an adhoc network

topology.

i. Scalability, ii. Controllability, iii. Store and Forward

2. Compare single hop and multihop networks topologies.

Single Hop Network                                      Multihop network

i. Routing Complexity is less                          Routing is more complicated.

ii. Information is transmitted only                  Store and forward facility is available.

once.

3. Name the five different cell types in the cellular hierarchy and compare them in terms of

Coverage area antenna site.

i. Femto cells, ii. Pico cells, iii. Micro cells, iv. Macro cells, v. Mega Cells

4. Why is hexagonal cell shape preferred over square or triangular cell shape to represent

the cellular architecture?

Because the hexagonal shape has the largest area for a given radius.

5. Name five architecture methods that are used to increase the capacity of an analog

Cellular system without increasing the number of antenna sites.

i.  Cell splitting

ii. Cell sectoring

iii. Lee’s Micro cell method

iv. Using Overlaid cells

v. Using smart antennas

6. Explain the following:

a. Cell splitting, b. Cell sectoring, c. Cell partitioning.

Cell Splitting:  In order to increase the number channels in an area the cells are splitted into smaller cells. This is called cell slitting.

Cell Sectoring:  Cell sectoring is done using directional antennas to increase the capacity of the cellular system. This method reduces the co channel interference.

Cell Partitioning: This technique increases the network capacity by cell partitioning. In this method channels are divided among larger macro cell and a smaller micro cell.

7. Explain how smart antennas can improve the capacity of cellular network.

Space division multiple access (SDMA) is used smart antennas. The directional antennas are very narrow. SDMA and narrow directional antennas reduce the co channel interference greatly. The sectored cells also reduce the reuse factor. Thus the smart antenna improves the capacity of a cellular network.

8. What are channel allocation techniques?

There are three channel allocation techniques. They are,

i.Fixed Channel Allocation

ii. Dynamic Channel Allocation

iii. Hybrid Channel Allocation

9. Explain the terms FCA, DCA, HCA.

FCA - Fixed Channel Allocation  : In this technique the entire bandwidth is divided among the channels in a cell permanently.

DCA –Dynamic Channel Allocation: Channel Allocation is done based on the load in the network.

HCA – Hybrid Channel Allocation: In this kind of Channel Allocation the channels are divided fixed  and dynamic sets and they are allocated accordingly.

10. Compare FCA and DCA.

Attribute                                FCA                                                    DCA

Traffic Load                            Better under heavy traffic                  Better under light traffic

Flexibility in channel               Low                                                     High

Allocation

Call setup delay                      Low                                                     Moderate/high

Control                                    Centralized                                          Centralized or Distributed.

11. Define channel borrowing technique and give its types.

The high traffic cells borrow the channels form the  low traffic cells in order to increase the system capacity. This is called channel borrowing. There are two types of channel borrowing: i. Static Channel borrowing and  ii. Dynamic Channel borrowing.

12. Define mobility management.

Location and Hand off management together are commonly referred to as mobility management.

13. Name the two important issues in mobility management.

i.Location Management and ii. Hand off Management

14. What is location management? What are the three components?

Location management refers to the activities a wireless network should perform in order to keep track of where the Ms is. The three components of mobility management are i. Location update algorithms, ii. Paging schemes, iii. Location information Dissemination

15. Name three paging mechanisms.

i. Blanket paging, ii. Closest – cells first paging, iii. Sequential paging

16. Explain about paging.

Paging is broadcasting a message in a cell or a group of cells to elicit a response from the MS for which a call or a message is incoming.

17. Mention the three traditional handoff techniques.

1. Hard handoff2.  Soft handoff

 

 

18. Difference between mobile controlled and mobile assisted hand off?

Mobile controlled hand off                           Mobile assisted hand off

i. Hand is controlled by the mobile                 Hand off is controlled by the network

nodes.                                                              and the mobile node.

19. Difference between centralized and distributed power control.

Centralized Power control                           Distributed Power control

i.Centralized power controller                  The mobile terminals individually

controls the power.                                         Adjust their power.

ii. Complexity is more.                                    Complexity is less.

20. What are the two steps in hand off?

i. Architectural issues in hand off

ii. Hand off decision time Algorithms

21. What are the privacy and authentication requirements of wireless networks?

In order to avoid the attack of unauthorized nodes in the network authentication is required in wireless networks.

22. How are public key and secret key algorithms different?

Secret key                                                       Public key

i. Same key is used for encryption                  Different keys are used for encryption

and decryption.                                               and decryption.

ii. They are  fast.                                             Not faster.

23. Explain the importance of key sizes in the security of an encryption algorithm?

When the key size is very small, it can be identified by eves by brute force method.But when key size is large it is very difficult to apply brute force method.

24. What is challenge response scheme?

This is used in IS 136 digital TDMA. The network generates a random number and sends it to the mobile terminal. The mobile terminal computes a value using the encryption algorithm. The value is transmitted over the air. The network computes its version of authentication and compares the two values. If the values match, the mobile terminal is identified.

25. What are the parts in location management?

i. Location updates  ii. Paging iii. Location information dissemination

UNIT III

WIRELESS WAN

PART –A ( 2 Marks)

1. Difference between registration and call establishment?

 

Registration                                                               Call establishment

During a registration procedure, network                   In mobile environment we have two

provides the MS with a channel for separate              separate call establishment  procedure

preliminary signaling.                                                  for mobile to fixed and fixed to mobile

                                                                                    Calls.

2. What are the reasons to perform handoff?

i. Signal strength deterioration, ii Traffic balancing, iii. Mobility of the terminal

3. Mention the different types of handoffs.

i. Mobile assisted hand off, ii. Network assisted hand off.

4. Difference between logical and physical channel?

Logical Channel                                                                    Physical channel       

Similar to computers, we need a set of           The physical layer specifies how the information

instructions and ports to instruct different     from different voice and data services are formatted

elements of the network to perform specific  into packets and sent through the radio channel.

duties. In telecommunications, these ports

 are called as logical channels.

5. Name five most important logical channels in GSM

1.Traffic Channels & 2 pilot channels

Types of  Traffic channels:

i. Full rate traffic channel & Half rate traffic channel

Types of Control channels:

i. Broadcast channels (BCH). ii. Common control Channels (CCCH) & Dedicated control channels(DCCH).

6. list the types of   stack layers.

i. Physical layer,  ii. Data link layer, iii. Networking or Messaging layer.

7. mention the types of bursts.

1. Normal burst, 2.  Frequency correction burst,3.  Synchronization burst, iv. Random access burst.

 

 

8. Mention the Three types of control channels.

i. Broadcast channels (BCH). ii. Common control Channels (CCCH) & Dedicated control channels(DCCH).

9. What is IS-95?

IS –95 is Interim Standards developed by TIA. Forward channel: 824-849 Mhz Reverse channel: 869-894 MHz .1.25 MHz/channel.

10. What is the  chip rats used in WCDMA?

WCDMA – Chip rate = 3.84 Mcps

11. How many physical channels are available in each IS-95 carrier? What type of coding

separates these channels from one another?

In IS – 95,  we have 64  physical channels. Walsh code is used to separate the channels.

12. Name the forward and reverse channels used in IS-95?

Forward Channels:

i. Pilot channel, ii. Synchronization channel, iii. Paging channel and Traffic channel

Reverse channels:

i. Access Channel, ii. Traffic channel, iii. Synchronization channel, iv. Paging channel

13. Difference between Walsh codes used in the forward and reverse channels of cdma

In reverse channels there is no spreading of the code. In reverse channel orthogonal codes are used for waveform encoding.

14. What are the bit rates of the data services supported by IS-95?

RS1:  9.6, 4.8, 2.4, & 1.2 kbps

RS2: 14.4,7.2,3.6, &1.8 kbps

15. Why is power control important in CDMA?

In CDMA the interference is from other users transmitting in the same frequency band at the same time. So in order to avoid near far effect and to maintain a good link quality it is necessary to control power in CDMA.

16. What forward channels are involved in IS-95 for power control?

Traffic channel  and control channel.

17. Why are several pilot channels monitored in IS-95? When does a pilot channels from a

base station move from an active set to a candidate set?

Several pilot channels are monitored in IS –95 in order to perform handoff. When the signal strength of the  pilot exceeds T-ADD it is transferred to a candidate set.

18. What are the new elements added to the GSM infrastructure to support GPRS?

GPRS uses the same physical radio channels and only new logical GPRS radio channels are defined.

19. What are different services offered by  GPRS?

i. Point to multi point, ii. Point to point

20. Name the connectionless and connection oriented services provided by the GPRS.

In GPRS Point to point communication, there are two types, i.  IP – connection less service, and ii. CLNP Connection oriented onX.25.

21. What is GPRS-136? How does it differ from GPRS?

The adaptation of GPRS to the IS –136 TDMA cellular standard is called GPRS-136.It uses 30kHz physical channel instead of 200KHz.

22. What is the importance of the framing hierarchy in GSM?

 A framing hierarchy is needed to identify the location of certain bursts among the large stream of bursts that are directed toward different terminals.

23. Name three sub systems in the GSM architecture.

Connection management, Mobility management, radio resource management.

24. What are VLR and HLR and why we need them?

VLR- Visitor Location Register, HLR – Home Location Register. They are used for mobility management.

UNIT IV

WIRELESS LAN

PART –A ( 2 Marks)

1. Name three categories of unlicensed bands used in U.S and compare them in terms of

size of the available band coverage.

ISM  is unlicensed  band used in U.S.

ISM Frequencies of operation : 902 –928 MHz, 2.4- 2.4835 GHz, 5.725 – 5.875 GHz.

2. Name the five major challenges for implementation of wireless LANs compare with one

another.

Single mac to support multiple physical layers. Mechanisms to allow multiple overlapping network in the same area. Provisions to handle the interference from other ISM band radios and

microwave ovens. Mechanism to handle ‘Hidden Terminals’. Options to support time bounded services. Provision to handle privacy and access control.

3. Explain the difference between wireless inter-LAN bridges and WLANs

A wireless bridge is a hardware component used to connect two or more network segments (LANs or parts of a LAN) which are physically and logically (by protocol) separated.

A wireless local area network (WLAN) links devices via a wireless distribution method (typically spread-spectrum or OFDM radio), and usually provides a connection through an access point to the wider internet

4. What are the differences between IEEE802.11 and HIPERLAN standards?

IEEE 802.11                                      HIPERLAN

WLAN is connectionless                    HIPERLAN-2 is connection oriented

Based on products                              HIPERLAN-1 is based on certain functional

                                                            Requirements.

5.What is WATM?

It  is wireless ATM.

6.Draw the frame format of WATM?

 

Wireless Header

 

ATM header

 

ATM payload

 

Wireless trailer

 

7. What are the responsibilities of the MAC management sub layer in 802.11?

The responsibilities of the MAC management sub layer are to define the access mechanisms and packet format, also it provides roaming support,power management and security.

8. What are the purpose of scrambler and interleaver in the HIPERLAN-2 modem?

In HIPERLAN – 2 modems, Scrambler is used to perform whitening process and interleaver is used to improve the reliability over temporal fading.

9. What is the purpose of guard time?

Guard time is to avoid overlapping of adjacent frames.

10. Similarities between the Medium access control of the HIPERLAN-2 and DECT.

Both  MAC layer  of HIPERLAN- 2 and DECT use TAMA/TDD access method. MT –MT  peer to peer transmission is also similar in both HIPERLAN- 2 and DECT.

 

11. What does  HiperLAN stands for?

High performance Radio LAN.It was initiated by RES10 group of ETSI as a PAN European standard for high speed wireless local network.

12.Specify requirements for HiperLAN1?

Data rates of 23.529Mbps Coverage of upto 100m Multihop Adhoc Networking capability Support of time bounded services Support of power saving

13. How many transport channels and logical channels are implemented in the HIPERLAN-2  DLC layer?

HIPERLAN-2  DLC layer has four  transport channels and five logical channels.

14. What is HAN?

HAN(Home Area Network) provides an infrastructure to interconnect a variety of home applications and enable them to access the Internet through a central home gateway.

UNIT-V

WPAN AND GEOLOCATION SYSTEMS

PART –A ( 2 Marks)

 

1. What is home RF?

Home RF working group is to provide th e foundation for a broad range of interoperable consumer devices by establishing an open industry specification for wireless digital communication between PC’s and consumer electronic devices anywhere in and around the home.

2. What is the IEEE 802.15 and what is the relation to the Bluetooth and homeRF?

The IEEE 802.15 WPAN group is focused on development of standards for short distance wireless networks used for networking of portable and mobile computing devices such as PC’s, PDA’s, cell phones, printers, speakers, microphones, and other consumer electronics. Home RF has a higher data rate than Bluetooth.

3. Name the four states that a Bluetooth terminal.

1. Master. (M) 2. Slave. (S)3. Stand By. (SB)4. Parked or hold. (P)

4. Name the three classes of application that are considered for Bluetooth technology?

1.  1. Cable replacement.2. Ad hoc personal network.3. Integrated AP.

5. Difference between 802.11 and 802.15.

IEEE 802.11 IEEE 802.15It is an independent standard to define PHY and MAC layers of WLAN.

It is focused on the standards for short distance Wireless networks used for networking of portable and mobile computing devices.

 

6. What is the maximum data rate of an overlay blue tooth network?

It allows a maximum data rate of 11 Mbit/s

7. Difference between the implementation of paging and inquiry algorithms in blue tooth?

With the paging procedure, an actual connection can be established. The paging procedure takes a very short time (at most 20 ms) while the inquiry procedure might cause a significant delay (up to a few seconds on average) The inquiry message is typically used for finding Bluetooth devices including publicprinters ,fax machines and similar devices with an unknown address.

8. Difference between GPS, wireless cellular assisted GPS, and indoor geo location

systems.

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense

Assisted GPS, generally abbreviated as A-GPS, is a carrier network dependent system which can, under certain conditions, improve the startup performance of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones

Indoor Geolocation is the process of finding geolocation of an electronic device inside a building

9. Differentiate between remote and self positioning systems.

In a self positioning system the MS locates its own position using measurements of its distance or its direction from known location of transmitter.

In remote positioning system recievers at known locations on a network together compute the location of a mobile transmitter usong the measurements of the distance of this mobile from each of the receivers.It is also called as network based or network centric positioning system.

10.What is WPAN?

Wpan is a short distance wireless networkused for networking of portable and mobile computing devices such as PCs, PDAs, cellphones, printers speakers…etc and other consumer electronics.

11.What is Bluetooth?

Bluetooth is an open specification for short range wireless voice and data communication that was originally developed for cable replacement in personal area networking to operate all over the world.

12.What are the requirements of WPAN?

Power management : Low current consumption. Range:0-10m Speed:19.2-100kbps Small size 0.5 cubic in without antenna Low cost relative to target device

13.What is SWAP?

 Shared wire access protocol it defines a new common interface that supports wireless voice and data networking in the home. The SWAP specification is an extension of DECT for voice and relaxed 802.11 for high speed  data applications.

14.Name the topology for blue tooth architecture?

 The topology of blue tooth is referred to as scattered adhoc topology. In scattered hoc environment a number of small network supports a few terminals to coexist or possibly interoperate with one another.