Wireless Communication MID TERM 2022

 Note : questions may repeat from mid term examination so be prepared

list various design issues for wireless network

Wireless networks can have a number of design issues, including: Interference: Interference from other wireless networks and electronic devices can negatively impact the performance of a wireless network. Range: The range of a wireless network is limited and can be impacted by obstacles such as walls and furniture. Bandwidth: Wireless networks must share bandwidth with other devices on the same frequency, which can lead to congestion and slow speeds. Security: Wireless networks are inherently less secure than wired networks, as wireless signals can be intercepted more easily. Power Management: Wireless devices rely on batteries and need to be designed with power management in mind to conserve energy and extend battery life. Roaming: Roaming from one access point to another can cause connection issues and interruptions in network coverage. Handoff: The process of handing off a device from one access point to another can also cause issues and cause interruptions in network coverage. Quality of Service: Ensuring quality of service (QoS) for different types of traffic, such as voice and video, can be a challenge in wireless networks. Capacity Planning: Designing a wireless network to meet capacity needs is a challenge, as it must be able to handle a large number of users and devices. Compatibility: Ensuring compatibility between different wireless devices and networks can be a challenge, as there are many different standards and protocols.

compare rayleigh & ricean fading and highlight thier key differences

Rayleigh fading and Ricean fading are two models that are used to describe the behavior of a wireless signal as it travels through the environment. Rayleigh fading is a statistical model that describes the behavior of a wireless signal in a multipath environment, where the signal is reflected by multiple surfaces and arrives at the receiver from multiple directions. In this model, the received signal is modeled as a sum of many randomly-phased components, resulting in a signal with a Gaussian distribution. Rayleigh fading is most commonly used in wireless systems that operate in environments with a large number of reflections, such as urban areas with many buildings. Ricean fading, on the other hand, is a statistical model that describes the behavior of a wireless signal in an environment with a strong line-of-sight (LOS) component and weaker multipath components. In this model, the received signal is modeled as a sum of a LOS component and a Rayleigh fading component, resulting in a signal with a Rice distribution. Ricean fading is most commonly used in wireless systems that operate in environments with a strong LOS component, such as rural areas with few buildings or open spaces. The key difference between Rayleigh fading and Ricean fading is the presence of a strong LOS component in Ricean fading. This results in a signal with a different statistical distribution and a lower variance, leading to improved signal quality and less signal fading. Another key difference is that Ricean fading is more appropriate for modeling wireless signals in environments with a strong LOS component, while Rayleigh fading is more appropriate for modeling wireless signals in environments with a large number of reflections.

write short note on IS-95 CDMA

IS-95 CDMA (Code Division Multiple Access) is a wireless communication technology that was standardized by the Telecommunications Industry Association (TIA) in the early 1990s. It is a multiple access technique that allows multiple users to share the same frequency band by encoding each user's data into a unique code. The receiver is then able to separate the signals from different users by decoding the unique codes. IS-95 CDMA is a 2G (second generation) wireless technology and was widely used in North America for mobile voice and data services. The technology was later replaced by 3G and 4G technologies, which offer higher data rates and improved performance. However, IS-95 CDMA continues to be used in some older wireless networks.

why GPRS has higher data rate as compared to GSM?

GPRS (General Packet Radio Service) is a wireless communication technology that provides faster data transfer rates than GSM (Global System for Mobile Communications). This is because GPRS uses packet switching instead of circuit switching, which allows multiple users to share the same network resources more efficiently. In GSM, each user is assigned a dedicated circuit for the duration of a call or data session, leading to lower utilization of network resources. In GPRS, data is broken into small packets and transmitted over the network, which allows multiple users to share the same resources more efficiently and results in higher data transfer rates. Additionally, GPRS also uses more advanced error correction and compression techniques, which further increases its data transfer rates compared to GSM.

If there is sudden increase in mobile users in a particular area like market for a short period of time, what are the ways through which mobile operator can provide uninterrupted services to them?

To provide uninterrupted services to mobile users in the event of a sudden increase in the number of users in a particular area, mobile operators can use the following strategies:

Increase network capacity: Mobile operators can temporarily increase network capacity in the affected area by deploying additional base stations, cell towers, or adding more bandwidth to the existing network.

Implement load balancing: Mobile operators can use load balancing techniques to distribute network traffic evenly across multiple base stations or cell towers, reducing congestion and ensuring that the network remains operational.

Use small cells: Mobile operators can deploy small cells, such as microcells or femtocells, to provide additional network coverage in areas with high user density. Small cells are low-power base stations that can be deployed quickly and easily to provide additional network capacity.

Use network offloading: Mobile operators can use network offloading techniques, such as Wi-Fi offloading, to reduce the load on their cellular network. Wi-Fi offloading allows mobile users to use Wi-Fi networks for data services, reducing the load on the cellular network and improving the overall quality of service.

Optimize network management: Mobile operators can optimize network management by using advanced network optimization techniques, such as traffic management and congestion control, to ensure that network resources are used efficiently and that the network remains operational even under high load conditions.

By implementing these strategies, mobile operators can provide uninterrupted services to users in areas with high user density and ensure that their networks remain operational even during periods of high traffic.

Explain PCS network architecture

CS (Personal Communications Service) network architecture refers to the overall design and organization of a wireless communication network that provides personal communications services. The architecture of a PCS network typically includes the following components: Base Stations: These are the radio transceivers that provide the connection between the mobile devices and the network. Base stations are responsible for transmitting and receiving signals to and from the mobile devices. Mobile Switching Centers (MSCs): These are the central control units that manage the flow of data and voice between the base stations and the public switched telephone network (PSTN). The MSCs also manage the authentication and billing of the mobile devices. Home Location Register (HLR): This is a database that stores information about each subscriber, including their phone number, service profile, and current location. The HLR is used by the MSC to determine the correct routing for incoming calls. Visitor Location Register (VLR): This is a database that is maintained by the MSC and contains information about the mobile devices that are currently located within its geographic area. The VLR is used to optimize the routing of calls and reduce the load on the HLR. Authentication Center (AuC): This is a secure database that stores information about each subscriber's authentication keys and profile. The AuC is used to authenticate and authorize the mobile devices when they attempt to access the network. Billing and Rating System: This system is responsible for collecting usage data and generating billing information for each subscriber. The billing and rating system interfaces with the MSCs and the HLR to obtain the necessary information for billing. In summary, the PCS network architecture is designed to provide reliable, efficient, and secure wireless communication services to mobile devices. The components of the PCS network work together to provide subscribers with seamless, real-time access to voice and data services.

explain mobility management in GSM

Mobility management in GSM (Global System for Mobile Communications) is the process of maintaining communication with a mobile device as it moves from one cell to another within a cellular network. The goal of mobility management is to ensure that a call or data session remains connected and that the user experiences seamless communication even as they move from one location to another. In GSM, mobility management is performed by the Mobile Switching Center (MSC) and the Home Location Register (HLR). The MSC is responsible for tracking the location of the mobile device and updating the HLR with the current cell location. The HLR is a central database that stores information about each subscriber, including their phone number, service profile, and current location. When a mobile device moves from one cell to another, the MSC updates the HLR with the new cell location. This allows the HLR to route incoming calls to the correct cell and ensures that the user experiences uninterrupted communication. The following are the key components of mobility management in GSM: Location Updating: This is the process of updating the HLR with the current cell location of a mobile device. Location updating is performed whenever the device moves from one cell to another. Handover: This is the process of transferring a call or data session from one cell to another as the mobile device moves from one location to another. Handover is performed seamlessly, ensuring that the user experiences uninterrupted communication. Authentication and Authorization: This is the process of verifying the identity of the mobile device and ensuring that it is authorized to access the network. Authentication and authorization are performed whenever the device attempts to access the network. In conclusion, mobility management in GSM is a crucial component of the overall network architecture. It ensures that mobile devices can move freely within the network and that users can experience seamless communication even as they move from one location to another.

explain the effects of multipath propogation on cdma

Multipath propagation is a phenomenon in wireless communication systems where a single radio signal can reach the receiver via multiple paths, due to reflections from buildings, trees, and other obstacles. In CDMA (Code Division Multiple Access) systems, multipath propagation can have both positive and negative effects. Positive effects of multipath propagation in CDMA: Diversity Gain: Multipath propagation can provide diversity gain, which helps to reduce the effects of fading and improve the overall quality of the radio link. When a signal arrives at the receiver via multiple paths, each path has a different amplitude and phase, which can help to average out the fading and improve the signal-to-noise ratio. Spatial Reuse: Multipath propagation can provide spatial reuse, which enables multiple users to share the same frequency band without interfering with each other. This is because the multiple paths of the signal can arrive at the receiver with different timing and phase, which can help to separate the signals of different users in the frequency domain. Negative effects of multipath propagation in CDMA: Interference: Multipath propagation can cause interference, which can degrade the performance of the CDMA system. When a signal arrives at the receiver via multiple paths, each path can have a different delay, which can cause the signals to interfere with each other. This can result in reduced signal quality and increased bit error rates. Timing Synchronization: Multipath propagation can make it more difficult to achieve timing synchronization, which is a crucial requirement for CDMA systems. When a signal arrives at the receiver via multiple paths, each path can have a different delay, which can make it difficult to accurately determine the timing of the signal. In conclusion, multipath propagation in CDMA systems can have both positive and negative effects on the performance of the system. The positive effects, such as diversity gain and spatial reuse, can help to improve the overall quality of the radio link, while the negative effects, such as interference and timing synchronization, can degrade the performance of the system. To mitigate the negative effects, advanced signal processing techniques, such as channel equalization, are often used in CDMA systems.

compare 3G and 4G wireless communication in terms of various parameters and technical specifications

3G (Third Generation) and 4G (Fourth Generation) are two generations of wireless communication technology that have different technical specifications and capabilities. Here is a comparison of 3G and 4G in terms of various parameters and technical specifications:

Data rate: 4G networks have much higher data rates compared to 3G networks. 4G networks typically provide data rates of up to 1 Gbps in the downlink and 100 Mbps in the uplink, while 3G networks provide data rates of up to 3-14 Mbps in the downlink and 1-5 Mbps in the uplink.

Latency: 4G networks have much lower latency compared to 3G networks. 4G networks typically have a latency of less than 100 milliseconds, while 3G networks have a latency of around 200-500 milliseconds.

Spectrum: 4G networks use wider bandwidths compared to 3G networks, which results in higher data rates and lower latency. 4G networks typically use bandwidths of 20 MHz or more, while 3G networks use bandwidths of 5 MHz or less.

Technology: 4G networks use advanced wireless technologies, such as Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) antennas, while 3G networks use less advanced technologies, such as Time Division Multiplexing (TDM) and Single-Input Single-Output (SISO) antennas.

Services: 4G networks support a wide range of advanced services, such as high-definition video conferencing, mobile TV, and cloud computing, while 3G networks support basic services, such as voice and text messaging.

Interoperability: 4G networks are designed to be highly interoperable with other wireless technologies, including Wi-Fi, while 3G networks are less interoperable.

Coverage: 4G networks typically have wider coverage compared to 3G networks, but the coverage of both technologies depends on many factors, such as the availability of spectrum, the density of the network, and the availability of infrastructure.

Parameters	3G	4G
Data rate (downlink)	3-14 Mbps	1 Gbps
Data rate (uplink)	1-5 Mbps	100 Mbps
Latency	200-500 ms	<100 ms
Spectrum	5 MHz or less	20 MHz or more
Technology	TDM and SISO antennas	OFDM and MIMO antennas
Services	Voice and text messaging	High-definition video conferencing, mobile TV, and cloud computing
Interoperability	Less interoperable	Highly interoperable with other wireless technologies, including Wi-Fi
Coverage	Dependent on many factors	Wider coverage compared to 3G, but dependent on many factors

compare slow fading with fast fading using table

Parameters	Slow Fading	Fast Fading
Time scale	Hours to days	Milliseconds to microseconds
Causes	Large-scale variations, such as shadowing, path loss, and multipath	Small-scale variations, such as multipath and reflection
Frequency	Low frequency	High frequency
Impact on signal	Gradual changes in signal strength and quality	Rapid and frequent changes in signal strength and quality
Effect on communication	Can result in significant reductions in signal quality and range	Can result in severe degradation of signal quality and result in packet loss

Given A certain city has an area of 1300 square miles and is covered by a cellular system using a seven cell reuse pattern. Each cell has a radius of 4 miles and the city has 40 mhz spectrum with a full duplex channel bandwidth of 60 khz. Find: (i) the number of cells in the service area. (ii) the number of channels per cell

(i) The number of cells in the service area can be calculated as follows:

A = π * r^2 = π * 4^2 = 16π

So the total number of cells in the service area = Total area of the city / Area of a cell = 1300 square miles / (16π square miles/cell) = 1300 / (16π) = 1300 / (50.27) = 25.7 approximately 26 cells

(ii) The number of channels per cell can be calculated as follows:

Number of channels per cell = Total available spectrum / Channel bandwidth = 40 MHz / 60 kHz = 666.67

So the number of channels per cell = 666.67

(iii) The total number of subscribers that can be served can be calculated as follows:

Number of subscribers per cell = Number of channels per cell / Reuse factor = 666.67 / 7 = 95.24 approximately 95 subscribers per cell

So the total number of subscribers that can be served = Number of subscribers per cell * Number of cells = 95 * 26 = 2470 subscribers.

Note : We want this many subscribers for GSS also :)