# Wireless communication technologies and design

### Abstract:

A radio coverage scenario has to be designed between 4 wireless nodes given as region, city, campus and in-building, according to the given conditions and assumptions which are given below.

### Conditions:

• All nodes share the same frequency.
• When in building transmits it can only be received by campus.
• When campus transmits both city and region can receive.
• when region transmits only city can receive.

### Assumptions:

• Each node has infant messages and wants to send to each of the other nodes if the message is not sent to the immediate neighbor then the message should be relayed.
• Time is slotted with a message transmission time taking exactly one time slot.
• During a slot a node can transmit, receive and can be idle.
• Collision occurs when two transmissions takes place. Assume no bit error.

### Introduction:

From the given scenario the network can be depicted as sown below.

In the coursework five tasks have been given with different cases in each of the task the maximum data rate has to be found. Therefore, each task will be examined separately as given below:

If a central manager controls the communication of these four nodes what is the maximum rate at which a data message can be transferred from node city to in building node given no other transfer has taken place during this transmission.

### Possible Solution:

In this case, the message at first needs to be sent from city to campus and then from campus to in-building. In order to send a message from the city to campus any radio access technologies can be used for example: GSM, EDGE, etc. so if we take edge into consideration the maximum data rate would be around 384 Kbps [3] access technologies can be used for example: GSM, EDGE, etc. so if we take edge into consideration the maximum data rate would be around 384 Kbps [3] for single carrier. Next after the signal is received by the campus node it can be transmitted to in building node using WIFI. In this case the maximum data rate would be around 54 Mbps for a single carrier.

If in building node sends a message to campus node and region to city. What is the combined maximum rate at which the data messages can flow from in building to campus and region to city?

### Possible Solution:

In the first case in building node needs to send a message to campus node this can be achieved by using WIFI and a maximum data rate would be around 54 Mbps [3] for a single carrier. In the next case the message needs to be sent from region to city. This can be achieved using GSM, EDGE, etc., so if we take edge into consideration the maximum data rate would be around 384 Kbps [3] for single carrier.

If campus node sends a message to node in building and city to region what is the combined max rate at which data message can flow from campus to in building and city to region

### Possible Solution:

In the first case a message needs to be sent from campus node to node in building this can be achieved using WIFI In this case the maximum data rate would be around 54 Mbps for a single carrier. In the second case a message has to be sent from city to region this can be achieved using GSM, EDGE etc., so if we take edge into consideration the maximum data rate would be around 384 Kbps [3] for single carrier.

Now suppose that the wireless link was not working and u replace it by wired link do questions 1-3 again using the wired link.

### Solution:

In this case the EDGE, GSM wireless technologies needs to be replaced by serial WAN links. The cables we use for serial WAN links are high bandwidth optical fibers with data rate of about 2.5Gbps [3] with 100Km spacing between the repeaters. Also, WIFI wireless technology needs to be replaced by ETHERNET/LAN links the cables we use for LAN links are Ethernet cables/ coaxial cables. Te data rates in this case might be from 1Gbps to 100Gbps [3].

Suppose now that you managed to fix the wireless link and you decide to use TCP to acknowledge messages sent from source to destination (destinations send acknowledgement).

### Solution:

Currently satellites offer a range of channel bandwidths, from the very small (a compressed phone circuit of a few kb/s) to the very large (the Advanced Communications and Telecommunications Satellite with 622-Mb/s circuits [3]). They also have a range of delays, from relatively small delays of low earth orbit (LEO) satellites to the much larger delays of GEO satellites. Our concern is making TCP/IP work well over those ranges [1].

Transmission Control Protocol (TCP) is a transport layer protocol which controls the transmission of data between two end nodes over an IP network. TCP has two primary functions: reliable delivery of data from sender to receiver, and active management of the transmission rate to avoid overly congesting the network. There are several schemes proposed to improve the performance of TCP over satellite links. Additional delay will be introduced due to TCP [2].

### Conclusion:

The above network scenarios can be achieved by using several communication technologies like WIMAX, HSPA, UMTS, LTE etc. It depends on the specifications of the network environment. Also in order to find out the exact data rates in each case all the parameters like bandwidth, signal to noise and interference ratio (SNIR) and TCP delay etc. have to be taken into consideration.

### References:

[1] Hashim Zafar, RaedA Abd-Alhameed, and Haseeb Zafar, "Performance comparison of TCP mechanisms over satellite networks", 2007 IEEE International Conference on Signal Processing and Communications (ICSPC 2007), 24-27 November 2007, Dubai, United Arab Emirates.

[2] Jing Wu 1 Yu Shi 2 Peng Zhang 1 Shiduan Cheng 1 Jian Ma 2, "ACK Delay Control for Improving TCP Throughput over Satellite Links"

[3] http://en.wikipedia.org/wiki/Spectral_efficiency#comparison_table

[4] WiMAX Forum,"Mobile WiMAX - Part II: A Comparative Analysis".

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