Unit V Cellular Standards

      Unit V – Cellular Standards

Part-A

1.Why the second generation was developed?

The second-generation  systems  have  been  developed  to  provide  higher  quality signals, higher data rates for support of digital services, and greater capacity.

2. What are second generation standards are available?

a)  Global system mobile (GSM) in Europe.

b)  IS 136 also Known as North American Digital Cellular (NADC) or US Digital

Cellular (USDC) in North America. c)   PDC in Japanese, TDMA standard.

d)  IS-95 in North America also known as cdma one.

3. Write the advantages 2G over 1G.

a)  Natural integration with the evolving digital wire line network. b)   Flexibility for capacity expansion.

c)  Reduction in RF transmits power.

d)  Encryption for communication privacy and e)   Reduction in system complexity.

f)   Higher data rate.

g)  Higher quality of signal and supports digital services.

4. What are the services offered by GSM?

GSM has defined three different categories of service

(i)        Telephone services

(ii)       Bearer (or) data services and

(iii)      Supplementary services.

5. Write about telephone service of GSM.

(i)        Teleservices provide communication between two and user applications according to a standard protocol.

(ii)       GSM mainly focuses on voice-oriented teleservices.

(iii)      This service including emergency calling and facsimile. (iv) GSM also supports videotext and teletex.

6. Write GSM features.

a)  Subscriber identity module(SIM) which is a memory devices that stores information such as the subscriber’s identification numbers, the networks and countries where the subscriber is entitled to service, privacy tags, and other user-specific information.

b)  GSM equipment manufacturer must sign the memorandum of understanding (MoU).

The MoU is an international agreement which allows the sharing of cryptographic algorithms and other proprietary information between countries and carriers.

7. What are the subsystems available in GSM system?

a) Base station subsystem (BSS)

b) Network and switching subsystem (NSS) and c)   Operation support subsystem(OSS)

8. What is the function of NSS in GSM?

`The NSS manages the switching functions of the systems and allows the MSCs to communicate with other networks such as the PSTN and ISDN.

9. What are the functions of OSS in GSM?

The OSS has three main functions

a)  To maintain the all telecommunications hardware and network operations with a particular market.

b)  Manage all charging and billing procedures and c)   Manage all mobile equipment in the system.

10. Define Abis interface.

The interface which connects a base transceiver station (BTS) to a base station controller (BSC) is called the Abis interface.

11.  Define A interface.

The interface between a BSC and a MSC is called the A interface, which is standardized within GSM.

12. Write the function of A-Interface.

a)  The A interface uses an SS7 protocol called the signaling correction control part (SCCP) which  supports communication between the MSC and the BSS, as well as network messages between the individual subscribers and the MSC.

b)  The  A  interface  allows  a  service  provider  to  use  base  stations  and  switching equipment made by different manufacturers.

13.  What are the databases available in NSS of GSM?

In the NSS, there are three different databases are used. They are

(i)        Home location register(HLR) (ii)      Visitor location register(VLR) (iii)   Authentication center (AuC).

14. Write the functions of HLR.

(i) The HLR is a database which contains subscriber information and location

Information for each user who resides in the same city as the MSC.

(ii) Each subscriber has international mobile subscriber identity (IMSI). This number is used to identify each home user.

 15. What is the function of VLR?

The VLR is a database which temporarily stores the IMSI and customer information for each roaming subscriber who is visiting the coverage area of a particular MSC.

16. Write the functions of AUV?

(i) The Authentication center is a strongly protected database which handles the authentication and encryption keys for every single Subscriber in the HLR and VLR.

(ii) The authentication center contains a register called the equipment identity register (EIR) which identifies stolen or fraudulently altered phones that transmit identity data that does not match which Information contained in either the HLR or VLR.

17. What are the basic channels available in GSM?

GSM specifies two basic groups of logical channels.

(i)         Traffic channels (TCHs) and

                        (ii)       Control channels (CCHs)

18. Write the types of TCH channels of GSM.

(i)         Full-rate TCH(TCH/F) and

(ii)        Half – rate TCH (TCH/H)

19. What are the control channels available in GSM?

There are three main control channels in the GSM system. They are

(i)        Broadcast channels (BCH)

(ii)       Common control channel (CCCH) (iii)            Dedicated control channel (DCCH)

20. Write the dedicated control channels available in GSM?

(a)     Stand-alone dedicated control channels (SDCCHs) (b)   Slow associated control channel (SACCH)

(c)     Fast associated control channels (FACCHs)

 21. What is the need guard period (Space).

The guard period is used to avoid overlapping with other bursts due to different path delays and to give the transmitter time to turn on and off.

22. Define DTM mode.

By incorporating a voice activity detector (VAD) in the speech coder, GSM systems operate in a  discontinuous transmission mode (DTM) which provides a longer subscriber battery life and reduces  instantaneous radio interference since the GSM transmitter is not active during silent periods.

23. What are the ciphering algorithms used in GSM?

(i) Two types of ciphering algorithms called A3 and A5   are used in GSM to prevent unauthorized network access and privacy for the radio transmission respectively.

(ii) The A3 algorithm is used to authenticate each mobile by verifying the user pass code within the SIM with the cryptographic key at the MSC.

(iii) The A5 algorithm provides the scrambling for the 114 coded data bit sent in each TS.

24. Define Burst Formatting in GSM.        

Burst formatting adds binary data to the ciphered blocks, in order to help synchronization and equalization of the received signal.

Mention the features of GSM.

(i)    DECT provides a cordless communications framework for high traffic density, short range telecommunications and covers a broad range of application and environments.

(ii)  DECT is configured around an open standard (OSI) which makes it possible to interconnect wide area fixed or mobile networks such as ISDN or GSM.

(iii) DECT provides low power radio access between portable parts and fixed base stations at ranges of up to a few hundred meters.

25. Write the applications of GSM.

(i) DECT offers excellent quality and services for voice and data applications.

(ii) It is to provide local mobility to portable users in an in-building private

Branch exchange (PBX)

                         (iii) It supports telephone services.

26. What are the channels in IS-95 supported by forward link?

The forward link supports four types of channels. (i) Pilot

(ii) Synchronization

(iii) Paging

(iv) Traffic

 27. What is the need of pilot channel?

The pilot channel is indented to provide a reference signal for all MSS within a cell that provides the phase reference for coherent demodulation.

28. What is the need of wide-band signaling in AMPS?

Wide-band data signaling may be used on a voice channel to provide brief data messages that allow the subscriber and the base station to adjust subscriber power or initiate a hand off.

29. Write the function of SAT in AMPS.

The particular frequency of the SAT denotes the particular base station location for a given channel and is assigned by the MSC for each call.

30. Mention any four parameters of AMPS.

Base station transmission band: 869 to 894 MHz. Mobile unit transmission band: 824 to 849 MHz.

Spacing between forward and reverse channels: 45 MHz. Channel bandwidth: 30 kHz.

31. Write the advantages of N-AMPS over AMPS.

N-AMPS provided three users in a 30 kHz AMPS channel by using FDMA and 10 kHz channels, and provided three times the capacity of AMPS.

32. What are the main objectives of the 3G system?

The objective of the 3G of wireless communication is to provide fairly high speed wireless communications to support multimedia, data and video in addition to voice.

33. Compare the CDMA systems.

Specification	IS-95 (Current System)	Cdma 2000 (U.S.A)	W-CDMA (Japan/Europe)
Channel	1.25 MHz	5MHz	5MHz
bandwidth
Number of carriers	1	3	1
Chip rate	1.2288 Mb/s	1.2288 Mb/s per carrier	4.096 Mb/s
Data rate	9.6 kb/s	Variable to 2 Mb/s	Variable to 2Mb/s

34. What is WLL?

Wireless local loops using radio transmission in the VHF and UHF bands have been employed in isolated areas for some time, because they can transmit signals for several kilometers without the need for stringing cable.

35. Write the advantages of WLL.

The WLL has a number of advantages over a wired approach to subscriber loop

Support.

Cost: WLL systems are less expensive than wired systems.

Intallation time: WLL system can be installed in a small fraction of the time required for a new wired system.

Selective installation: Radio units are installed only for those subscribers who want the service at a given time.

36. Define Pico net.

The simplest Bluetooth networks called piconets can have from two to eight nodes. A piconet is a collection of Bluetooth devices which are synchronized to the Same hoping sequence.

37. What is Bluetooth?

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

38. What is scatter net?

One Bluetooth devices can operate simultaneously on two piconets, acting As a bridge between the two. A conglomeration of two or more piconets is called a Scatter net.

39. Define load.         

Traffic intensity across the entire trunked radio system, measured in Erlangs.

40. What is request rate?

The average number of call requests per unit tie. It is denoted by λ seconds-1.

41. What are the techniques used to improve received signal quality and link performance?

                                   (i)        Equalization

(ii)       Diversity

(iii)      Channel coding

42. Define reflection effect.

If an object is large compared to the wavelength of the signal, e.g., huge buildings, mountains or the surface of the wavelengths, the signal is reflected.

The reflected signal is not as strong as the original, as objects can absorb some of the signals power.

43. What are the drawbacks available direct RF pulse systems?

(i) Due to the usage of wide pass band filter for multipath resolution, the System is easily affected by interference and noise.

(ii)If the first arriving signal is blocked or fades, serve fading occurs, and the system may not trigger properly.

(iii)Due to the use of an envelope detector, the phases of the individual multipath components are not received.

(iv)The coherent detector permits measurement of the multipath phase using this technique.

PART B

1. Write short notes on:

           (i) EDGE Standard

           (ii) IS-95B Standard

2. Discuss in detail about forward and reverse CDMA channel.

3. With the channel and frame structure, explain in detail about GSM architecture.

4. Explain in detail about W-CDMA architecture.

5. Give an overview about advanced mobile phone service

6. Explain in detail about AMPS

7. Explain about GPRS