Chapter-4 Fundamental Concepts of Wireless Communication PDF

Chapter-4 Fundamental Concepts of Wireless Communication By:- Tesfalidet Ketema (SW Engir.)  Outline Overview of Wireless Comm. Wireless - Advantages Vs Disadvantages Basic Elements of a Wireless Comm. System Electromagnetic Spectrum in Wireless Communication Terms in M...

Chapter-4 Fundamental Concepts of Wireless Communication By:- Tesfalidet Ketema (SW Engir.)  Outline Overview of Wireless Comm. Wireless - Advantages Vs Disadvantages Basic Elements of a Wireless Comm. System Electromagnetic Spectrum in Wireless Communication Terms in Mobile Telephony Wireless Communication - Multiple Access Overview of Cellular System By:- Tesfalidet Ketema (SW Engir.) 2  Overview of Wireless Comm. Wireless Communication is an advanced branch of communication engineering. Wireless communication involves the transmission of information over a distance without the help of wires, cables or any other forms of electrical conductors. Wireless communication is a broad term that incorporates all procedures and forms of connecting and communicating between two or more devices using a wireless signal through wireless communication technologies and devices. By:- Tesfalidet Ketema (SW Engir.) 3  Cont’d… Generally, in a wireless communication system, information is transmitted from transmitter to receiver that are placed over a limited distance. With the help of Wireless Communication, the transmitter and receiver can be placed anywhere between few meters (like a T.V. Remote Control) to few thousand kilometers (Satellite Communication). We live in a World of communication and Wireless Communication, in particular, is a key part of our lives. Some of the commonly used Wireless Communication Systems in our day – to – day life are: Mobile Phones, GPS Receivers, Remote Controls, Bluetooth Audio and Wi-Fi etc. By:- Tesfalidet Ketema (SW Engir.) 4 Examples of Wireless Comm. Modules By:- Tesfalidet Ketema (SW Engir.) 5  Features of Wireless The evolution Comm. of wireless technology has brought many advancements with its effective features. The transmitted distance can be anywhere between a few meters (for example, a television's remote control) and thousands of kilometers (for example, radio communication). Wireless communication can be used for cellular telephony, wireless access to the internet, wireless home networking, and so on. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, By:-headphones, Tesfalidet Ketema (SW Engir.) radio receivers,6  Wireless - Advantages Wireless communication involves transfer of information without any physical connection between two or more points. Because of this absence of any 'physical infrastructure', wireless communication has certain advantages. This would often include collapsing distance or space. Wireless communication has several advantages; the most important ones are − Cost effectiveness Wired communication entails the use of connection wires. In wireless networks, communication does not require elaborate physical infrastructure or maintenance practices. Hence the cost is reduced. Example − Any company providing wireless 7 communication services does not incur a lot of By:- Tesfalidet Ketema (SW Engir.)  Cont’d… Flexibility Wireless communication enables people to communicate regardless of their location. It is not necessary to be in an office or some telephone booth in order to pass and receive messages. Miners in the outback can rely on satellite phones to call their loved ones, and thus, help improve their general welfare by keeping them in touch with the people who mean the most to them. Convenience Wireless communication devices like mobile phones are quite simple and therefore allow anyone to use them, wherever they may be. There is no need to physically connect anything in order to receive or pass messages. Example − Wireless communications services can also be seen in Internet technologies such as Wi-Fi. With no network cables hampering movement, we can now By:- Tesfalidet Ketema (SW Engir.) 8  Cont’d… Speed Improvements can also be seen in speed. The network connectivity or the accessibility were much improved in accuracy and speed. Eg:- A wireless remote can operate a system faster than a wired one. Accessibility The wireless technology helps easy accessibility as the remote areas where ground lines can’t be properly laid, are being easily connected to the network. Eg:- Online education is now possible. Constant connectivity Constant connectivity also ensures that people can respond to emergencies relatively quickly. Example − A wireless mobile can ensure you a By:- Tesfalidet Ketema (SW Engir.) 9 constant connectivity though you move from place  Wireless - Disadvantages Even though wireless communication has a number of advantages over wired communication, there are a few disadvantages as well. The most concerning disadvantages are Interference, Security and Health. Interference Wireless Communication systems use open space as the medium for transmitting signals. As a result, there is a huge chance that radio signals from one wireless communication system or network might interfere with other signals. The best example is Bluetooth and Wi-Fi (WLAN). Both these technologies use the 2.4GHz frequency for communication and when both of these devices are active at the same time, there is a chance of interference. By:- Tesfalidet Ketema (SW Engir.) 10  Cont’d… Security One of the main concerns of wireless communication is Security of the data. Since the signals are transmitted in open space, it is possible that an intruder can intercept the signals and copy sensitive information. Health Concerns Continuous exposure to any type of radiation can be hazardous. Even though the levels of RF energy that can cause the damage are not accurately established, it is advised to avoid RF radiation to the maximum. By:- Tesfalidet Ketema (SW Engir.) 11 Basic Elements of a Wireless Comm. System A typical Wireless Communication System can be divided into three elements: the Transmitter, the Channel and the Receiver. Fig:- Block diagram of wireless By:- Tesfalidetcommunication Ketema (SW Engir.) system 12  Cont’d… 1. Transmission Path A typical transmission path of a Wireless Communication System consists of Encoder, Encryption, Modulation and Multiplexing. The signal from the source is passed through a Source Encoder, which converts the signal in to a suitable form for applying signal processing techniques. The redundant information from signal is removed in this process in order to maximize the utilization of resources. This signal is then encrypted using an Encryption Standard so that the signalBy:-and the information is secured Tesfalidet Ketema (SW Engir.) 13 and doesn’t allow any unauthorized access.  Cont’d… Channel Encoding is a technique that is applied to the signal to reduce the impairments like noise, interference, etc. During this process, a small amount of redundancy is introduced to the signal so that it becomes robust against noise. Then the signal is modulated using a suitable Modulation Technique (like PSK, FSK and QPSK etc.) , so that the signal can be easily transmitted using antenna. The modulated signal is then multiplexed with other signals using different Multiplexing Techniques like Time Division Multiplexing (TDM) or Frequency Division14 By:- Tesfalidet Ketema (SW Engir.)  Cont’d… 2. Channel The channel in Wireless Communication indicates the medium of transmission of the signal i.e. open space. A wireless channel is unpredictable and also highly variable and random in nature. A channel maybe subject to interference, distortion, noise, scattering etc. and the result is that the received signal may be filled with errors. 3. Reception Path The job of the Receiver is to collect the signal from the channel and reproduce it as the source signal. The reception path of a Wireless Communication System comprises of Demultiplexing , Demodulation, Channel Decoding, Decryption and Source Decoding. From the components of the reception path it is clear that the task of the receiver is just the inverse to that of transmitter. By:- Tesfalidet Ketema (SW Engir.) 15  Cont’d… The signal from the channel is received by the Demultiplexer and is separated from other signals. The individual signals are demodulated using appropriate Demodulation Techniques and the original message signal is recovered. The redundant bits from the message are removed using the Channel Decoder. Since the message is encrypted, Decryption of the signal removes the security and turns it into simple sequence of bits. Finally, this signal is given to the Source By:- Tesfalidet Ketema (SW Engir.) 16 Decoder to get back the original  Electromagnetic Spectrum in Wireless Communication Wireless communication relies on electromagnetic waves for transmitting data. The electromagnetic spectrum encompasses a range of frequencies, from low-frequency radio waves to high-frequency gamma rays. Different wireless technologies utilize specific frequency bands within this spectrum, each offering distinct advantages in terms of coverage, bandwidth, and propagation characteristics. Wireless communication takes places over free space through RF (radio frequency), one device, a Transmitter, sends signal to another device, a Receiver. Two devices (transmitter and receiver) must use same frequency (or channel) to be able to communicate with each other. If a large number of wireless devices By:- communicate at same time, radio Tesfalidet Ketema (SW Engir.) 17  18 By:- Tesfalidet Ketema (SW Engir.)  Cont’d… Wireless devices share airtime just like wired devices connect to shared media and share common bandwidth. For effective use of media, all wireless devices operate in half duplex mode to avoid collision or interference. Before the transmission begins, devices following IEEE 802.11 standard must check whether channel is available and clear. Note Wireless communication is always half duplex as transmission uses same frequency or channel. To achieve full duplex mode, devices use different frequency or channel of transmission and receiving of signals. You can say that wireless communication is Full duplex By:- Tesfalidet Ketema (SW Engir.) 19  Electromagnetic Cont’d… waves are measured by wavelength and frequency. Wavelength is the distance covered by one complete cycle of the electromagnetic wave. Frequency is the number of electromagnetic waves in one second, also known as a Hertz or Hz. One Hz By:- Tesfalidet Ketema (SW Engir.) equals one cycle per second. One megahertz (MHz) equals one million cycles per second. Generally, microwaves are radio frequencies measuring more than 1 GHz. Example 20  Cont’d… By:- Tesfalidet Ketema (SW Engir.) Fig: Electromagnetic spectrum 21  Terms in Mobile Telephony Mobile Station (MS) − The Mobile Station (MS) communicates the information with the user and modifies it to the transmission protocols of the air interface to communicate with the BSS. The user information communicates with the MS through a microphone and speaker for the speech, keyboard and display for short messaging and the cable connection for other data terminals. The mobile station has two elements Mobile Equipment (ME) and Subscriber Identity Module (SIM). Mobile Equipment (ME) − ME is a piece of hardware that the customer purchases from the equipment manufacturer. The hardware piece contains all the components needed for the implementation of the protocols to interface with the user and the air-interface to the base stations. By:- Tesfalidet Ketema (SW Engir.) 22  Cont’d… Subscriber Identity Module (SIM) − This is a smart card issued at the subscription to identify the specifications of a user such as address and type of service. The calls in the GSM are directed to the SIM rather than the terminal. By:- Tesfalidet Ketema (SW Engir.) SMS are also stored in the SIM card. It carries every user's personal information which enables a number of useful applications. Base Station (BS) − A base station transmits and receives user data. When a mobile is only responsible for its user's data transmission and reception, a base station is capable to handle the calls of several subscribers simultaneously. Base Transceiver Station (BTS) − The user data transmission takes place between the 23  Cont’d… Mobile Switching Center (MSC) − MSC is the hardware part of the wireless switch that can communicate with PSTN switches using the Signaling System 7 (SS7) protocol as well as other MSCs in the coverage area of a service provider. The MSC also provides for communication with other wired and wireless networks as well as support for registration and maintenance of the connection with the mobile stations. The following image illustrates the parts of different sub-systems. HLR, VLR, EIR and AuC are the sub- systems of Network sub-system. By:- Tesfalidet Ketema (SW Engir.) 24  Cont’d… 25 By:- Tesfalidet Ketema (SW Engir.)  Cont’d… Channels − It is a range of frequency allotted to particular service or systems. Control Channel − Radio channel used for transmission of call setup, call request, call initiation and other beacon or control purposes. Forward Control Channel(FCC) − Radio channel used for transmission of information from the base station to the mobile Reverse Channel(RC) − Radio channel used for transmission of information from the mobile to base station. Voice Channel(VC) − Radio channel used for voice or data transmission. Handoff − It is defined as the transferring a call from the channel or base station to another base station. Roamer − A mobile station which operates in a service area other than that from which service has been subscribed Transceiver − A device capable of simultaneously transmitting and receiving radio signals. 26 By:- Tesfalidet Ketema (SW Engir.) Wireless Comm. - Multiple Access Multiple access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum. Multiple Access Techniques In wireless communication systems, it is often desirable to allow the subscriber to send information simultaneously from the mobile station to the base station while receiving information from the base station to the mobile station. A cellular system divides any given area into cells where a mobile unit in each cell communicates with a base station. The main aim in the cellular system design is to be able 27 to increase the capacity of the channel, i.e., By:- Tesfalidet Ketema (SW Engir.)  Cont’d… There are several different ways to allow access to the channel. These includes mainly By:- Tesfalidet Ketema (SW Engir.) the following − – Frequency division multiple-access (FDMA) – Time division multiple-access (TDMA) – Code division multiple-access (CDMA) – Space division multiple access (SDMA) 28  Cont’d… Narrowband Systems Systems operating with channels substantially narrower than the coherence bandwidth are called as Narrow band systems. Narrow band TDMA allows users to use the same channel but allocates a unique time slot to each user on the channel, thus separating a small number of users in time on a single channel. Wideband Systems In wideband systems, the transmission bandwidth of a single channel is much larger than the coherence bandwidth of the channel. Thus, multipath fading doesn’t greatly affect the received signal within a wideband channel, and frequency By:-selective fades occur only in a Tesfalidet Ketema (SW Engir.) 29  Frequency Division Multiple Access (FDMA) FDMA is the basic technology for advanced mobile phone services. The features of FDMA are as follows. FDMA allots a different sub-band of frequency to each different user to access the network. If FDMA is not in use, the channel is left idle instead of allotting to the other users. FDMA is implemented in Narrowband systems and it is less complex than TDMA. Tight filtering is done here to reduce adjacent channel interference. The base station BS and mobile station MS, transmit and receive simultaneously and continuously in By:- FDMA. Tesfalidet Ketema (SW Engir.) 30 Time Division Multiple Access (TDMA) In the cases where continuous transmission is not required, there TDMA is used instead of FDMA. The features of TDMA include the following. TDMA shares a single carrier frequency with several users where each users makes use of non-overlapping time slots. Data transmission in TDMA is not continuous, but occurs in bursts. Hence handsoff process is simpler. TDMA uses different time slots for transmission and reception thus duplexers are not required. TDMA has an advantage that is possible to allocate different numbers By:- Tesfalidet of time slots per Ketema (SW Engir.) 31 Code Division Multiple Access (CDMA) Code division multiple access technique is an example of multiple access where several transmitters use a single channel to send information simultaneously. Its features are as follows. In CDMA every user uses the full available spectrum instead of getting allotted by separate frequency. CDMA is much recommended for voice and data communications. While multiple codes occupy the same channel in CDMA, the users having same code can communicate with each other. CDMA offers more air-space capacity than TDMA. The hands-off between base stations is very well handled by CDMA. By:- Tesfalidet Ketema (SW Engir.) 32  Space Division Multiple Access (SDMA) Space division multiple access or spatial division multiple access is a technique which is MIMO (multiple-input multiple-output) architecture and used mostly in wireless and satellite communication. It has the following features. All users can communicate at the same time using the same channel. SDMA is completely free from interference. A single satellite can communicate with more satellites receivers of the same frequency. The directional spot-beam antennas are used and hence the base station in SDMA, can track a movingBy:-user. Tesfalidet Ketema (SW Engir.) 33 Overview of Cellular System By:- Tesfalidet Ketema (SW Engir.) 34  Cellular Wireless Networks Cellular network is an underlying technology for mobile phones, personal communication systems, wireless networking etc. The technology is developed for mobile radio telephone to replace high power transmitter/receiver systems. Cellular networks use lower power, shorter range and more transmitters for data transmission. By:- Tesfalidet Ketema (SW Engir.) 35 Features of Cellular Systems Wireless Cellular Systems solves the problem of spectral congestion and increases user capacity. The features of cellular systems are as follows − Offer very high capacity in a limited spectrum. Reuse of radio channel in different cells. Enable a fixed number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region. Communication is always between mobile and base station (not directly between mobiles). By:- Tesfalidet Ketema (SW Engir.) 36  Cont’d… Each cellular base station is allocated a group of radio channels within a small geographic area called a cell. Neighboring cells are assigned different channel groups. By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells. Keep interference levels within tolerable limits. Frequency reuse or frequency planning. Organization of Wireless Cellular Network. By:- Tesfalidet Ketema (SW Engir.) 37  Cellular Network Organization Multiple low power transmitters – 100w or less Area divided into cells – Each with own antenna – Each with own range of frequencies – Served by base station Transmitter, receiver, control unit – Adjacent cells on different frequencies to avoid crosstalk By:- Tesfalidet Ketema (SW Engir.) 38  Shape of Cells The coverage area of cellular networks are divided into cells, each cell having its own antenna for transmitting the signals. Each cell has its own frequencies. Data communication in cellular networks is served by its base station transmitter, receiver and its control unit. The shape of cells can be either square or hexagon. Square 2d A square cell has four neighbors at distance d and four at distance Root – Better if By:- Tesfalidet all Ketemaadjacent (SW Engir.) antennas 39  Cont’d… Hexagon A hexagon cell shape is highly recommended for its easy coverage and calculations. Provides equidistant antennas Radius defined as radius of circum-circle – Distance from center to vertex equals length of side Distance between centers of cells radius R is 3R Not always precise hexagons – Topographical limitations – Local signal propagation conditions – Location of antennas 40 By:- Tesfalidet Ketema (SW Engir.) Cellular Geometries By:- Tesfalidet Ketema (SW Engir.) 41  Frequency Reuse Frequency reusing is the concept of using the same radio frequencies within a given area, that are separated by considerable distance, with minimal interference, to establish communication. Frequency reuse offers the following benefits − – Allows communications within cell on a given frequency – Limits escaping power to adjacent cells – Allows re-use of frequencies in nearby cells – Uses same frequency for multiple conversations – 10 to 50 frequencies per cell 42 By:- Tesfalidet Ketema (SW Engir.)  Cont’d… Example:- –N cells all using same number of frequencies –K total number of frequencies used in systems – Each cell has K/N frequencies – Advanced Mobile Phone Service (AMPS) K=395, N=7 giving 57 frequencies per cell on average By:- Tesfalidet Ketema (SW Engir.) 43 Frequency Reuse Patterns By:- Tesfalidet Ketema (SW Engir.) 44