The document discusses the Global System for Mobile Communications (GSM), detailing its specifications, features, and advantages over analogue systems, including increased capacity, improved audio quality, and security measures. It outlines GSM's use of specific radio frequencies, cellular telephony structure, and various services such as voice and data connections, highlighting its importance in the mobilization of communication. Additionally, the document explores advanced concepts like backscatter communication, its types, and performance metrics in relation to future Internet of Things (IoT) scenarios.

1. UNIT 5
GSM
By : Dr. Tushar S. Muratkar, PhD

2. INTRODUCTION TO
GSM
INTRODUCTION
⦿ The Global System for Mobile Communications (GSM) is a set of recommendations
and specifications for a digital cellular telephone network (known as a Public Land
Mobile Network, or PLMN).
⦿ These recommendations ensure the compatibility of equipment from
different GSM manufacturers, and interconnectivity between different
administrations, including operation across international boundaries.
⦿ GSM networks are digital and can cater for high system capacities.
⦿ They are consistent with the world-wide digitization of the telephone network, and
are an extension of the Integrated Services Digital Network (ISDN), using a digital
radio interface between the cellular network and the mobile subscriber equipment.
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3. CELLULAR TELEPHONY
⦿ A cellular telephone system links mobile subscribers into the public telephone
system or to another cellular subscriber.
⦿ Information between the mobile unit and the cellular network uses radio
communication. Hence the subscriber is able to move around and become fully
mobile.
⦿ The service area in which mobile communication is to be provided is divided into
regions called cells.
⦿ Each cell has the equipment to transmit and receive calls from any subscriber
located within the borders of its radio coverage area.
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4. GSM FREQUENCIES
⦿ GSM systems use radio frequencies between 890-915 MHz for receive and
between 935-960 MHz for transmit.
⦿ RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for use.
⦿ An RF carrier is a pair of radio frequencies, one used in each direction.
⦿ Transmit and receive frequencies are always separated by 45 MHz.
4
890 960
935
915
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ

5. GSM FEATURES
INCREASED CAPACITY
⦿ The GSM system provides a greater subscriber capacity than analogue systems.
⦿ GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair
comprising one transmit channel and one receive channel).
⦿ Digital channel coding and the modulation used makes the signal resistant to interference
from cells where the same frequencies are re-used (co-channel interference); a Carrier to
Interference Ratio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with
analogue cellular.
⦿ This allows increased geographic reuse by permitting a reduction in the number of cells in
the reuse pattern.
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6. AUDIO QUALITY
⦿ Digital transmission of speech and high performance digital signal processors provide good
quality speech transmission.
⦿ Since GSM is a digital technology, the signals passed over a digital air interface can be
protected against errors by using better error detection and correction techniques.
⦿ In regions of interference or noise-limited operation the speech quality is noticeably better
than analogue.
USE OF STANDARDISED OPEN INTERFACES
⦿ Standard interfaces such as C7 and X25 are used throughout the system. Hence different
manufacturers can be selected for different parts of the PLMN.
⦿ There is a high flexibilty in where the Network components are situated.
6

7. IMPROVED SECURITY AND CONFIDENTIALITY
⦿ GSM offers high speech and data confidentiality.
⦿ Subscriber authentication can be performed by the system to check if a subscriber is a
valid subscriber or not.
⦿ The GSM system provides for high degree of confidentiality for the subscriber. Calls are
encoded and ciphered when sent over air.
⦿ The mobile equipment can be identified independently from the mobile subscriber. The
mobile has a identity number hard coded into it when it is manufactured. This number is
stored in a standard database and whenever a call is made the equipment can be checked
to see if it has been reported stolen.
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8. CLEANER HANDOVERS
⦿ GSM uses Mobile assisted handover techique.
⦿ The mobile itself carries out the signal strength and quality measurement of its server and
signal strength measurement of its neighbors.
⦿ This data is passed on the Network which then uses sophisticated algorithms to determine
the need of handover.
SUBSCRIBER IDENTIFICATION
⦿ In a GSM system the mobile station and the subscriber are identified separately.
⦿ The subscriber is identified by means of a smart card known as a SIM.
⦿ This enables the subscriber to use different mobile equipment while retaining the same
subscriber number.
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9. FREQUENCY REUSE
⦿ There are total 124 carriers in GSM ( additional 50 carriers are available if EGSM band is
used).
⦿ Each carrier has 8 timeslots and if 7 can be used for traffic then a maximum of 868 ( 124 X
7 ) calls can be made. This is not enough and hence frequencies have to be reused.
⦿ The same RF carrier is used for many conversations in several different cells at same time.
⦿ The radio carriers available are allocated as per regular pattern which repeats over
the whole coverage area.
⦿ The pattern to be used depends on traffic requirement and spectrum availability.
⦿ Some typical repeat patterns are 4/12, 7/21 etc.
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6
4
3
7
2
5
1
2
1

10. GSM SERVICES
• GSM offers several types of connections
• voice connections, data connections, short message service
• multi-service options (combination of basic services)
• Three service domains
• Bearer Services
• Telematic Services
• Supplementary Services

11. GSM SERVICES
Tele services:
⦿ GSM mainly focuses on voice-oriented tele services via mobile phones.
⦿ All these basic services have to obey cellular functions, security measurements etc.
⦿ These comprise encrypted voice transmission, message services, basic data
communication with terminals as known from the PSTN or ISDN (e.g., fax).
⦿ Another service offered by GSM is the emergency number (eg 911, 999).
⦿ This service is mandatory for all providers and free of charge.
⦿ This connection also has the highest priority, possibly pre-empting other connections,
automatically be set up with the closest emergency center.

12. GSM SERVICES
• Additional services
⦿ Non-Voice-Teleservices such as group 3 fax, voice mailbox (implemented in the fixed
network supporting the mobile terminals) , electronic mail (MHS, Message Handling
System, implemented in the fixed network).
⦿ A useful service for very simple message transfer is the short message service (SMS)
alphanumeric data transmission to/from the mobile terminal (160 characters) using the
signaling channel .
⦿ Sending and receiving of SMS is possible during data or voice transmission.
⦿ It can be used for “serious” applications such as displaying road conditions, e-mail headers
or stock quotes, but it can also transfer logos, ring tones, horoscopes and love letters.

13. GSM SERVICES
⦿ Bearer Services:
⦿ Data services or Bearer Services are used through a GSM phone.
⦿ To receive and send data is the essential building block leading to widespread mobile
Internet access and mobile data transfer.
⦿ GSM currently has a data transfer rate of 9.6k. New developments that will push up data
transfer rates for GSM users are HSCSD (high speed circuit switched data) and GPRS
(general packet radio service) are now available.

14. ⦿ Supplementary :
⦿ Supplementary services are additional services that are provided in addition to teleservices
and bearer services. These services include caller identification, call forwarding, call waiting,
multi-party conversations, and barring of outgoing (international) calls, among others.
• Conferencing It allows a mobile subscriber to establish a multiparty conversation, i.e., a
−
simultaneous conversation between three or more subscribers to setup a conference call. This
service is only applicable to normal telephony.
• Call Waiting This service notifies a mobile subscriber of an incoming call during a conversation.
−
The subscriber can answer, reject, or ignore the incoming call.
• Call Hold This service allows a subscriber to put an incoming call on hold and resume after a
−
while. The call hold service is applicable to normal telephony.
• Call Forwarding Call Forwarding is used to divert calls from the original recipient to another
−
number. It is normally set up by the subscriber himself. It can be used by the subscriber to divert
calls from the Mobile Station when the subscriber is not available, and so to ensure that calls are
not lost.
• Call Barring Call Barring is useful to restrict certain types of outgoing calls such as ISD or stop
−
incoming calls from undesired numbers. Call barring is a flexible service that enables the

15. Self introduction
15
Current Designation : Sr. project engineer at IIT Bombay (18th
Jul 2022).
Specific Project : Next Generation Wireless
Research and Standardization on 5G.
Education : BE (Pune Univ.), MTECH
(Nagpur Univ.), PhD in Wireless
Communication from IIITN, Nagpur
(2022).
Experience : 4 years teaching ,
4 years research (PhD).
Hobbies : Playing cricket, table
tennis, exercising, listening
motivational speaker
Family Info : 5 members.

16. Why do I want to join
MathWorks ?
16
Accelerat
ed
engineerin
g &
science
sector
Flagship
products:
MATLAB,
Simulink,
toolboxes,
etc
Multidimensi
onCore
Values
Working
with
MathWor
ks clients

17. Why training engineer at MathWorks ?
17
Passion for
teaching.
• First job in
teaching.
• Worked as
T&P
coordinator.
Helps to stay
upgraded with
new
MathWorks
products/
technologies.
.Allows to do
computational
analysis and
simulations.
Opportunity
to discuss with
customers
during
projects.

18. Technical part:
18
Learning outcome
Present and future internet of things (IoT)
scenario.
Backscatter communication (BakComm), its
types and architecture.
Analyze the BakComm system in MATLAB.

19. Trends in short range IoT
communication
19
• By 2027, the total number of short range IoT devices => 22.4 billion [1].
• Que. Could you please mention different short range IoT protocols ?
Short range IoT protocols
Bluetoot
h
Ultra
wide
band
(UWB)
Zigbee Wi-Fi

20. 20
Fig 1. Power consumption by different short range wireless
communication standards [2]

21. 21
• All of these consumes more power and so may not be suitable for
future IoT.
• Is it possible to have extremely less power consumption, in micro
watt ?
• Yes, and the solution is BakComm system.
Problem
statement

22. BakComm Systems :
22
• BakComm is a method that uses an incident radio-frequency (RF)
signal to transmit data without a battery or power source.
Fig 2 a) Tag Fig 2 b)

23. Types of BakComm :
23
Fig 3 . Classification of BakComm
System

24. 1) MoBC system
⦿ Receiver and RF source (carrier
emitter) are located within the
reader.
⦿ The tag modulates and reflects
the RF signals coming from the
RF source.
⦿ Limitation: Short range
24
Reader
(RF source +
Receiver)
Tag
Downlink signal
Uplink
signal
Fig 4. MoBC
System

25. 2) BiBC system
⦿ The RF source and the
backscatter receiver are
separated.
⦿ Thus increases range.
⦿ Limitation: Dedicated RF
source is needed.
25
Backscatter
receiver
Tag
Backscattered
signal
Fig 5. BiBC System
RF Source
(dedicated)

26. 3) AmBC system
⦿ It uses ambient RF source.
⦿ Advantages:
• Low cost
• Improves spectrum utilization.
⦿ Challenges: Less stable than
BiBC.
26
Backscatter
receiver
Tag
Backscattered
signal
Fig 6. AmBC
System
Ambient RF
Source

27. Analysis of AmBC system
27
1) Performance metrics in AmBC:
Performance
SNR
BER
Outage
Probabilit
y

28. No. of error bits out of
total bits transmitted.
28
Bit error rate
(BER)
SNR of particular link
is below threshold value.
Outage
Probability
Ratio of signal power to
noise power.
Signal to
Noise ratio
(SNR)

29. 2) Choice of tool for analysis:
29
Cost effective
Analyze system
over long period
of time
System can be
studied more
closely
Avoid danger
situations
• Hence we choose MATLAB for
Strong
documentation &
online support

30. 3) Hardcoding of wireless channel:
30
• The wireless channels are random in nature.
• Hence, the channels between RF source-tag, RF source-reader
and tag-reader are random.
• Random quantities follows different distributions: Gaussian,
Exponential, Rayleigh, Nakagami, etc with their mean and
variance.
• We considered the Rayleigh distribution.
where
• MATLAB Code :
X = random('norm', 0, sqrt(2)); % normal RV 1
Y = random('norm', 0, sqrt(2)); % normal RV 2

31. 4) Novel AmBC system model :
Fig 7. Multi-tag AmBC system in time-selective
fading
31

32. %% Initialization
al = 0.5; % alpha, backscattering coefficient
t1 = 10^4; % Number of iterations
n = 5; % signalling instant
sig2_e_mun= 0; % variance related to estimation error
sig2_k = 1; % variance of channel between RF source to tag
sig2_hn = 1; % variance of channel beteen source to reader
sig2_gn = 10; % variance of channel between tag to reader
gamma_th_dB = 3; % threshold
gamma_th = 10^(gamma_th_dB/10); % dB to linear conversion
sig2_mun = ((sig2_hn)+ ((al^2)*sig2_k*sig2_gn));% variance of combined
channel
L = 2; % number of tags
5) MATLAB Code
32

33. %% Correlation Parameter Calculation
vel_r =10; % 20 miles per hour is speed of reader and it is 8.9408 mps.
c = 3*10^8; % speed of light
fc = 1.9*10^9; % carrier frequency in GHz
Rs = 9.6 *10^3; % data rate
Z = ((2*pi*fc*vel_r)/(Rs*c));
P_mun = besselj(0,Z); % rho i.e., correlation parameter
c3 = (P_mun)^(2*(n-1));
v_phi_mun = (1-c3)*sig2_mun;% variance of nodes mobility noise
%% Looping
op = []; count = 0;
for j1 = -5:5:15 % Avg transmit snr i.e., gammabar in dB
jj1 = 10^(j1/10); dB to linear conversion
33

34. for t = 1:t1 % number of iterations
t % for observing values of t
mun1 = sqrt(sig2_mun/2)*(randn(1,L)+1i*randn(1,L)); % Step 5,
complex Gaussian
mun1_abs = abs(mun1); % Step 5 % Rayleigh
mun1_abs_sq = (mun1_abs).^2; % Step 5
A = (c3*mun1_abs_sq); %Step 4
B = (v_phi_mun); %Step 4
C = (c3*sig2_e_mun); %Step 4
gamma1 = ((A)/(B+C+(1/jj1))); % Step 3
gamma_s = max(gamma1); % Step 2, we choose selection combining
diversity
34

35. SNRdB = -5:5:15; % Avg transmit snr i.e., gammabar
if gamma_s < gamma_th % Step 1: definition of outage probability
count = count+1;
end
end
op = [op,count/(t)]; % appending the calculated outage probability
count = 0;
end
%% plotting
grid on;
semilogy(SNRdB,op,'g-','LineWidth',1.1); % semilog plot on y axis
title('Outage Probability for changes in SNR'); % title of plot
ylabel('Outage Probabilty'); % y axis label
xlabel('average ytansmit SNR') % x axis label 35

36. 1 Multiple tags.
2 Moving
nodes.
3 Different speed of nodes
4 Number of tags
5 Estimation error
6) Novelty and Contributions
36

37. 7) Results :
Fig 8. Outage probability versus average SNR for different number of
tags 37

38. Fig 9. Outage probability versus average SNR for different speed, L = 4
38

39. Fig 10. Outage probability versus average SNR for different estimation
error, L = 4 39

40. Conclusion
Need
and
types of
Bakcom
m system
Choosing
a
simulati
on tool
Hardcodin
g in
MATLAB
Key
Performanc
e metrics
in AmBC
Results
Novelty and
Contributions
40

41. References:
[1] S. O’Dea, “Number of wide-area and short-range iot devices worldwide
from 2014 to 2026,” https://www.statista.com/statistics/1016276/wide-
area-and-short-rangeiot-device-installed-base-worldwide/, accessed:
2022-01-28.
[2] R. Mubashar, M. A. B. Siddique, A. U. Rehman, A. Asad, and A. Rasool,
“Comparative performance analysis of short-range wireless protocols for
wireless personal area network,” Iran Journal of Computer Science, vol. 4,
no. 3, pp. 201–210, 2021.
41

42. THANK YOU!!
You can find me at:
⦿ https://www.linkedin.com/in/tushar-s-muratkar-phd-
b6062520/
⦿ tushar_16m@yahoo.co.in
⦿ 8208566797
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