Mobile Communications Lecture 6 PDF

Mobile Communications Lecture - 6 ELCN434 ELCn434 ELC 534 Dr. Refaat Mohamed Copyright Dr.Refaat Mohamed 1  Learning Outcomes 1- Discover different Mobile Communications systems. 2- Define the different requirements for each mobile commu...

Mobile Communications Lecture - 6 ELCN434 ELCn434 ELC 534 Dr. Refaat Mohamed Copyright Dr.Refaat Mohamed 1  Learning Outcomes 1- Discover different Mobile Communications systems. 2- Define the different requirements for each mobile communications system (Bit rate, Range, operating frequency, BER, ….. ). 3- Technical challenge in Mobile Communications systems. 4- Cellular concept and frequency re-use. Copyright Dr.Refaat Mohamed 2  Learning Outcomes 5- Channel frequency assignment. 6- Trunking theorem and cellular system design and performance evaluations. 7- Interference calculations and cellular system design.(Co-channel interference and Adjacent channel Interference). 8- Different methods to increase system capacity (Cell splitting-Cell sectoring- zone controllers). Copyright Dr.Refaat Mohamed 3  Learning Outcomes 9- Different propagation models used in indoors and outdoors communications. 10 – Fading margin calculations used in cellular system design. 11- Range design and Coverage design in cellular mobile communication systems. 12- Multiple access techniques (FDMA-TDMA-CDMA- OFDMA-SDMA-PR). 13- Impact of different modulation techniques in Mobile communication techniques 14- Analyze 5G cellular systems and beyond. Copyright Dr.Refaat Mohamed 4 Improving Coverage and System Capacity What is System Capacity? C = M k N, Where N is the Cluster Size, k is the number of Channels used per Cell, and M is the Replications of the the Cluster in the given System Coverage Area. In terms of Traffic Intensity, we know that total Traffic handled by a System is A = U Au, U is the number of users in the System, and Au is the traffic generated by a typical user. Max. Value that A can assume is C [Upper Limit of the System]. From A = U Au, we can easily Conclude that as U increases, A will increase, so the Traffic Offered to the System will Increase Leading to Congestion [Blockage of the Calls]. Given an Allocated Spectrum [S = k N ] which is Fixed, We have to use some Cellular Design Techniques to Improve System Capacity [ C or A as A is a Function of C]. Copyright Dr.Refaat Mohamed 5 Improving Coverage and System Capacity Cellular Design Techniques to Improve System Capacity 1- Cell Splitting Technique: This Technique Improves the System Capacity by Reducing the Cluster Coverage Area [ in other words Cell Area] to Increase M, keeping Cluster Size N and Co-Channel Reuse Ratio, Q = D/R = SQRT(3N) Constant. It Maintains S/I by Reducing the Base Station Tx Power, Antenna Height, and Antenna Down-Tilting Mechanism. 2- Sectoring Technique: This Technique Improves the system Capacity by Reducing the Cluster Size, N, to get High value of M. Since it plays with N, thus, Changing Q and S/I. In order to use same Cell Size and Tx Power, it has to use Cell Sectoring to Avoid Co-Channel Interference by using Directional Antennas. It Improves System Capacity and S/I but at the Cost of Decreased System Trunking Efficiency. 3- Microcell Zone Technique: This is the Latest Technique which Improve the System Capacity and S/I without Compromising at System Trunking Efficiency. Copyright Dr.Refaat Mohamed 6 Improving Coverage and System Capacity 1- Cell Splitting Technique Any Congested Cell is Splitted into several Smaller Cells called uCells. C Cell [uCell] Coverage Area is D E Reduced -> Cluster Area is G D Reduced that in turn Increase M, E B so Improvement in System F F D Capacity is Achieved. C A F Placement of the uCells is Made C C E G such that it Maintains the System B Frequency Reuse Structure/Plan. G D E Q and S/I is Maintained by B Reduction in Tx Power, Antenna Height, G and Using Antenna Down-Tilting F Technique. Copyright Dr.Refaat Mohamed 7 Improving Coverage and System Capacity Cell Splitting Technique C How much Reduction of Tx Power? E D Pr (old Cell Boundary)  Pt1 R-n G D Pr (new Cell Boundary)  Pt2 (R/r)-n F E B F D C A F Equating them, we get Pt2 = Pt1 / rn C C Where r is splitting factor. E G B For Urban Environment, n = 4, G D E Cells are splitted by half B so. Pt2 = Pt1 / 16 or 12 dB down. G F Copyright Dr.Refaat Mohamed 8 Improving Coverage and System Capacity System Growth in Cell Splitting In the beginning, only the Congested Cells are Splitted. Different Cell Sizes in Use Demands for Different Frequency/Channel Groups and Tx Power/ Antenna Height. Size of Channel Groups Depends on the Splitting Stage. Bigger Cells are used for High Speed Traffic As the Demand Increases in Micro-cells and With More Cells get Splitted, , uCell Channel Group is made Relatively Bigger. As Splitting gets Completed, all Cells are of the same Size and Use the Entire Frequency Spectrum according to the Frequency Reuse Plan. Copyright Dr.Refaat Mohamed 9 Improving Coverage and System Capacity Copyright Dr.Refaat Mohamed 10 Improving Coverage and System Capacity Copyright Dr.Refaat Mohamed 11 Improving Coverage and System Capacity 2- Sectoring Technique: Improves the System Capacity by Reducing the Cluster Size, N(keeping the Cell Size same), to 2-1 get more Cell Cluster Replications. 2-3 2-2 3-1 As N is decreased, Q = D/R = 3-3 2-1 1-1 3-2 2-3 1-3 SQRT(3N), is also decreased. 2-2 3-3 3-1 1-2 4-3 4-1 As the Cell Size is kept the same, the 1-3 1-1 3-2 4-2 1-2 Tx 4-3 4-1 4-2 Power of the BS is to be kept the same. That will Increase the Chances of Co- Channel Interference. 1 6 2 To Improve S/I (by reducing I), we use 5 4 3 Cell Sectoring and Use Directional Antennas. 1- 120 Degree Sectoring [3 Freq. Groups. 2- 60 Degree Sectoring [6 Freq. Groups] Copyright Dr.Refaat Mohamed 12 Improving Coverage and System Capacity Sectoring Technique: Each Cell in the Cluster is Divided into 3/6 Sectors Each Sector uses a Smaller Group of Channels Reduced Trunking Efficiency With Sectoring and Use of Directional Antennas, Interference is Reduced. S/I is Improved. Number of Handoff is Increased Many Modern Systems, Within a Cell, Inter-Sector Handoff are dealt by the Mobile sets without Involving MSC. In Short, Increase in System Capacity and S/I is Achieved at the Cost of Reduction of Trunking Efficiency. Copyright Dr.Refaat Mohamed 13 Improving Coverage and System Capacity 3- Microcell Zone Technique: Improves the System Capacity as well as S/I ratio without Sacrificing the Trunking Efficiency of the System. All Microcell Zones [3 or more in a Cell] use a Single Base Station but Different Tx/Rx Equipment with Reduced Tx Power. All the Channels are Placed in a Pool at the BS and Equally Shared by all uCell Zones [ No subdivision of Channels as against in Sectoring] The Antennas of Each Zone Tx/Rx are Directed inwards and Placed at the Outer Edge of the Cell. Cell Maintains its Coverage Area, Co- Channel Interference is Reduced. Copyright Dr.Refaat Mohamed 14