1. Wireless Network PMIT- By-
Jesmin Akhter
Associate Professor
Institute of Information Technology
Jahangirnagar University

2. Lecture 06 Wireless Sensor Networks Mobile Cellular Network

3. Wireless Sensor Networks

4. Definition
A sensor network is an infrastructure comprised of sensing (measuring), computing, and communication elements. The results acquired by a regional network is provided to the administrator.
The administrator observe and react to events/phenomena in a specified environment. The administrator typically is a civil, governmental, commercial, or industrial entity.
The environment can be the physical world (temperature, pressure, sound), a biological system (biological and chemical sensors for national security applications for example Air pollution monitoring, Water quality monitoring) or an information technology (IT) framework.

5. There are four basic components in a sensor network:
An assembly of distributed or localized sensors;
An interconnecting network (usually, but not always wireless-based);
A central point of information clustering; and
A set of computing resources at the central point (or beyond) to handle data correlation, event trending, status querying, and data mining.

6. Characteristics of a WSN
Self Organization
Concurrency processing
Low cost
Restricted energy resources
Tiny
Small radio range
Characteristics

7. Applications
A wide-range of applications offered by WSN, some of these are environmental monitoring, industrial sensing, infrastructure protection, battlefield awareness and temperature sensing.
Military applications
Monitoring inimical forces
Monitoring friendly forces and equipment
Military-theater or battlefield surveillance
Targeting
Battle damage assessment
Nuclear, biological, and chemical attack detection
and more . . .
Environmental applications
Microclimates
Forest fire detection
Flood detection
Precision agriculture

8. Health applications
Remote monitoring of physiological data
Tracking and monitoring doctors and patients inside a hospital
Drug administration
Elderly assistance
and more . . .
Home applications
Home automation
Instrumented environment
Automated meter reading
Commercial applications
Environmental control in industrial and office buildings
Inventory control
Vehicle tracking and detection
Traffic flow surveillance

9. Infrastructure of Sensor Networks
The region being sensed is normally partitioned into equally loaded clusters of sensor nodes, as shown in Figure 2. A cluster in a sensor network resembles a domain in a computer network. In other words, nodes are inserted in the vicinity of a certain predefined region, forming a cluster. Different types of sensors can also be deployed in a region.
In Figure 2, three clusters are interconnected to the main base station, each cluster contains a cluster head responsible for routing data from its corresponding cluster to a base station.
Figure 2. A sensor network and its clusters

10. The wireless sensor node is equipped with a limited power source, such as a battery or even a solar cell, where there is enough sun light exposure on the node. However, a solar cell may not be the best choice as a power supply, owing to its weight, volume, and expense. In some application scenarios, sensor-node lifetime depends on the battery lifetime.

11. Sensor Node Structure Fig.3 A typical wireless sensor node
Figure 3 shows a typical sensor node. A node consists mainly of 3 components: sensing unit, a processing unit and memory, a self-power unit.
Other supporting components are: wireless transceiver component, as well as a self- and remote-testing unit, a synchronizing and timing unit, a routing table, and security units.
Each node must determine its location. This task is carried out by a location-finding system based on the global positioning system (GPS).
Fig.3 A typical wireless sensor node

12. Sensing Unit
The sensing unit consists of a sensor and an analog-to-digital converter. A smart sensor node consists of a combination of multiple sensors.
The analog signals produced by the sensors, based on the observed event, are converted to digital signals by the converter and then fed into the processing unit.

13. Processing and Memory Unit
The processing unit performs certain computations on the data and, depending on how it is programmed, may send the resulting information out to the network.
The processing unit, which is generally associated with memory, manages the procedures that make the sensor node collaborate with the other nodes to carry out the assigned sensing task.
The central processor determines what data needs to be analyzed, stored, or compared with the data stored in memory.

14. Self-Power Unit
A sensor node is supposed to be mounted in a small physical unit, limiting space for the battery. Moreover, the random distribution of sensors makes it impossible to periodically recharge or exchange batteries.
In most types of sensor networks, the power unit in a sensor node is the most important unit of the node because the liveliness and existence of a node depend on the energy left in the node, and the routing in the sensor network is based on the algorithm that finds a path with the least energy.
Thus, it is essential to use energy-efficient algorithms to prolong the life of sensor networks. The main task of the sensor node is to identify events, to process data, and then to transmit the data. The power of a node is consumed mainly in the transmitter and receiver unit.
The sensor node can be supplied by a self-power unit, self-power unit battery, or solar cells

15. Clustering Protocols
Clustering Protocols specify the topology of the hierarchical non-overlapping cluster nodes.
An efficient Clustering Protocol ensures the creation of clusters with almost the same radius and cluster heads that are the best positioned in the cluster.
Since every node in a cluster network is connected to cluster head, route discovery among cluster heads is sufficient to establish a feasible route in the network.

16. Classification of Clustering Protocols
Clustering techniques can be either centralized or decentralized.
Centralized clustering algorithms require each sensor node to send its individual information, such as energy level and geographical position, to the central base station. Based on a predefined algorithm, a base station calculates the number of clusters, their sizes, and the cluster heads' positions and then provides each node with its newly assigned duty.
Decentralized clustering techniques create clusters without the help of any centralized base station. An energy-efficient and hierarchical clustering algorithm can be such a way whereby each sensor node becomes a cluster head with a probability of p and advertises its candidacy to nodes that are no more than k hops away from the cluster head.
The Low-Energy Adaptive Clustering Hierarchy (LEACH) algorithm and the Decentralized Energy-Efficient Cluster Propagation (DEEP) protocol are two examples of the decentralized clustering protocols.

17. 1. LEACH Clustering Protocol
The Low-Energy Adaptive Clustering Hierarchy (LEACH) is an application-specific protocol architecture that aims to prolong network lifetime by periodic re-clustering and change of the network topology.
LEACH is divided into rounds consisting of a clustering phase and a steady-state phase for data collection. At the start of each round, a sensor node randomly chooses a number between 0 and 1 and then compares this number to a calculated threshold called T(n). If T(n) is larger than the chosen number, the node becomes a cluster head for the current round. The value T(n) is calculated using the following formula:
where p is the ratio of the total number of cluster heads to the total number of nodes, r is the number of rounds, and G is a set of nodes that have not been chosen as cluster heads for the last 1/p rounds.

18. Tn =p./(1-p*(mod(r,1/p))); plot(r,Tn, 'b>-') xlabel('r')
ylabel('T(n)')
grid on
r =
Tn =

19. For the first round (r = 0), T(n) is equal to p, and nodes have an equal chance to become cluster head. As r gets closer to 1/p, T(n) increases, and nodes that have not been selected as cluster head in the last 1/p rounds have more chance to become cluster head.

20. After 1/p - 1 rounds, T(n) is equal to 1, meaning that all the remaining nodes have been selected as cluster head. Thus, after 1/p rounds, all the nodes have had a chance to become a cluster head once. Since being the cluster head puts a substantial burden on the sensor nodes, this ensures that the network has no overloaded node that runs out of energy sooner than the others.
After cluster heads are self-selected, they start to advertise their candidacy to the other sensor nodes.
When a node receives advertisements from more than one cluster-head, chooses the candidate whose associated signal is received with higher power. This ensures that sensor node chooses the closest candidates as cluster head.

21. 2. DEEP Clustering Protocol
The Decentralized Energy-Efficient Cluster Propagation (DEEP) protocol that establishes clusters with uniformly distributed cluster heads. This protocol balances the load among all the cluster heads by keeping the clusters' radii fairly equal. This protocol is completely decentralized, and there is no need for any location-finder device or hardware.
The protocol starts with an initial cluster head and forms new cluster-head candidates gradually by controlling the relative distance between a pair of cluster heads and the circular radius of each cluster.

22. In order to avoid the frequent control signal transmission and extra power consumption associated with that, a cluster head can be placed at the center of the cluster and cluster members can send the data packets directly to the cluster head without the need for any route set-up protocol.
In order to explain the details of this algorithm, control signals and protocol parameters need to be introduced:
Control signals: (1) cluster-head declaration signal or (2) cluster-head exploration signal
Membership search signal with control parameters: declaration range (dr), exploration range (dr1, dr2), minimum number of members (mn), the received signal energy (Erc1 and Erc2).

23. DEEP forms clusters by starting with an initial cluster head that can be chosen prior to network deployment. This initial cluster head starts the cluster set-up phase by propagating cluster-head declaration signals within the range of dr. (This means that the cluster-head candidate chooses an appropriate data rate and signal output power so that it can reach nodes that are less than dr away from the sender) At this point, sensor nodes that receive the declaration signal accept the corresponding cluster head as a leader.

24. Begin DEEP Clustering Algorithm
Initial cluster head finds cluster members by sending "cluster-head declaration.”
Initial cluster head finds new cluster-head candidates by sending "cluster-head exploration signal.”
Repeat: Cluster-head candidates that are placed on the (dr1, dr2) ring find cluster members.
Nodes that receive more than one cluster-head declaration choose the closest cluster head, based on the received signal energy.
Cluster-head candidates that receive a cluster-head declaration signal negotiate with the sender, and one of them gets eliminated.
Confirmed cluster heads send "cluster-head exploration" signals to find new cluster-head candidates(Go to step 4).
Finalize: If the number of members in a cluster is less than mn, all the members find new clusters by sending the membership-search signal.
At the end, a node that has not received any control signal sends the membership-search signal.

25. Mobile Cellular Network

26. Cell
Concept of mobile cellular communication system has arises from cell.
Cell is the unit coverage of mobile cellular network.
Geographic area is divided into cells, each serviced by an antenna and its associated radio equipment called base station (BS).
The hexagonal cells are arranged in a continuous fashion to cover the entire service.
Hexagonal cell

27. Basic of Mobile Cellular Network
Hexagonal Cells in a continuous fashion
Break the metropolitan area into small areas
Each area is approximated with a hexagonal cell.
A base station is located at the center of each cell.
Each cell is assigned only a fraction of the total number of channels.
Cells that are sufficiently far apart can reuse the same frequency.

28. Why Hexagonal Cell?
Hexagonal-shaped communication cells are artificial and that such a shape cannot be generated in the real world. Engineers draw hexagonal-shaped cells on a layout to simplify the planning and design of a cellular system because it approaches a circular shape that is the ideal power coverage area. The circular shapes have overlapped areas which make the drawing unclear. The hexagonal shaped cells fit the planned area nicely with no gap and on overlap between the cells. The real cell has irregular shape because of natural, and man made obstacle in service area. R R R
Cell R R
(a) Ideal cell
(b) Actual cell
(c) Different cell models
Factitious

29. Factitious
Idealized Coverage
Footprint
Reality!

30. Basic Mobile Cellular Communication System
Cell phones communicate with Base Station over wireless links, called the ‘air interface’.
Base Stations connected to MTSO/MSC to switch calls to/from cell phone users
The base station is the bridge between the mobile users and the MSC via telephone lines or microwave links. Mobile Switching Center (MSC) controls several BSs and serves as gateway to the backbone network (PSTN, ISDN, Internet).
Circuit-switched is a type of network in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Ordinary voice phone service is circuit-switched. The telephone company reserves a specific physical path to the number you are calling for the duration of your call. During that time, no one else can use the physical lines involved.
Integrated Services Digital Network(ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.

31. Mobile cellular network
MSC
PSTN
The Mobile Telephone Switching Office (MTSO) is the mobile equivalent to a PSTN Central Office. The MTSO contains the switching equipment or Mobile Switching Center (MSC) for routing mobile phone calls. It also contains the equipment for controlling the cell sites that are connected to the MSC.
Mobile cellular network

32. Cell Clusters
Service areas are normally divided into clusters of cells to facilitate system design and increased capacity.
Cell clusters are used in frequency planning for the network
The pattern of cluster is repeated throughout the network.
Entire BW is used within a cluster.
Coverage area of cluster called a ‘footprint’

33. Definition
Cells in a cellular network are generally “grouped” together into cell clusters. Cellular networks are generally designed as a repeated cluster pattern The number of cells in a cluster (typically 4,7, 12 or 21) is a trade-off between the traffic capacity in the cluster and its interference with the adjacent cluster of cells (where the same frequencies will be re-used) 1 2 5 6 7 4 3

34. Frequency Reuse Cluster-2 2 2 1 5 Cluster-1 1 5 4 4 3 7 3 7 6 6 2 1 5

35. Cell Pattern N = 4 2 1 3 2 4 2 3 1 3 1 4 2 4 1 3 4

36. Frequency Reuse Distance
The minimum distance which allows the same frequency to be reused will depend on many factors such as the number of co-channel cells in the vicinity of the center cell, the type of geographic land outline, antenna height and the transmitted power at each cell site.

37. Frequency Reuse 7 cell reuse cluster F1 F2 F3 F4 F5 F6 F7
Reuse distance D
7 cell reuse cluster

38. Reuse Distance Cluster RF1 F2 F3 F4 F5 F6 F7
Reuse distance D R
Cluster
For hexagonal cells, the reuse distance is given by
where R is cell radius and N is the reuse pattern (the cluster size or the number of cells per cluster).
Reuse factor is

39. Determine two parameters i and j, called shift parameters
Starting from any cell, move i cells along any one of the six emanating chains of hexagons. Turn clock (or counter clock)-wise by 60 degree and then move j cells along the chain. The destination is the nearest co-channel cell
By repeating this pattern, clusters of cells are formed such that each cell within a cluster is assigned a different set of frequencies. Such a cluster is called a frequency reuse pattern.

40. Example-2 where i = 2, j = 1 Note: i and j are integers =7
Reuse factor
i = 2, j = 1
Note: i and j are integers =7

41. Example-1 A
Shift Parameter: i = 3, j = 2
= 19

42. If all the cell sites transmit the same power then N increases and the frequency reuse distance D increases. This increased D reduces the chance that the co-channel interference may occur. Theoretically a large N is desired. However the total number of allocate channel is fixed. When N is too large, the number of channel assigned to each of N cells becomes small and carried traffic of that cell will be smaller.

43. Interferences In Mobile Cellular Network
Co-site Channel Interferences
Adjacent Channel Interferences
Co-channel Channel Interferences

44. Co-site Channel Interferences
Mutual interferences created by the users inside a cell is called co-site channel interferences. Since users are very closed in cell therefore separation between carries within a cell should be wide enough to avid interferences. At the same time uplink and down link carriers of an user are separated by 45MHz.

45. Adjacent Channel Interferences
Interferences created by the users of two adjacent cells are called adjacent channel interferences. Because of small distance between adjacent cells an wide band gap should be maintained between carries of adjacent cell to avoid interferences.

46. Co-channel Interferences
Interferences created by the users of two co-channel cells are called co-channel interferences. Because of use of same carries, huge interference is created despite of long distance between to co-cell. The distance between co-cell increases with increase in N, the of cells in a cluster.
Co-channel and adjacent channel interferences can be reduced using sectored cells.

47. Co-channel Interference
Determine the minimum distance at which a frequency can be reused with no interference, called the co-channel reuse distance (D).
Signal-to-interference ratio, (C / I), is an index of channel interference. A
Shift Parameter: i = 3, j = 2

48. First tier co-channel Base Station Second tier co-channel Base Station
Mobile Station D2 D3
Serving Base Station

49. Worst Case of Co-channel InterferenceD6 R D5 D1
Mobile Station D4 D2 D3
Serving Base Station
Co-channel Base Station

50. Co-channel Interference
Co-channel interference ratio is given by
where I is co-channel interference and M is the maximum number of co-channel interfering cells. We know,
C α R-γ
Therefore C=K. R-γ; where K is a constant and γ is path loss slope,
 = 2~5, Similarly, Ik = K. Dk-γ
For M = 6, C/I is given by, å = ÷ ø ö ç è æ M k R D 1 I C -g

51. TYPES OF TRANSMISSION MODE
Simplex Transmission Mode.
Half Duplex Transmission Mode
Full Duplex Transmission Mode.

52. SIMPLEX MODE
In simplex mode transmission information sent in only one direction.
Device connected in simplex mode is either sent only or received only that is one device can only send, other device can only receive.
Communication is unidirectional.

53. HALF DUPLEX
In half duplex transmission data can be sent in both the directions, but only in one direction at a time.
Both the connected device can transmit and receive but not simultaneously.
When one device is sending the other can only receive and vice-versa.

54. FULL DUPLEX
In full duplex transmission, data can be sent in both the directions simultaneously.
Both the connected devices can transmit and receive at the same time.
Therefore it represents truly bi-directional system.
In full duplex mode, signals going in either
Direction share the full capacity of link.

55. Thank You