# TELE4652
## Generations of communications systems
Each generation has a set of requirements - any technology that fulfils these requirements you can say is part of that generation.
- [1G](../Concepts/Telecommunications/1G.md)
- [2G](../Concepts/Telecommunications/2G.md)
- [3G](../Concepts/Telecommunications/3G.md)
- [4G](../Concepts/General/4G.md)
- [5G](../Concepts/General/5G.md)
## Switching Standards
- G - [GPRS](../Concepts/General/General%20Packet%20Radio%20Services.md)
- E - [enhanced data rates for GSM evolution](../Concepts/General/enhanced%20data%20rates%20for%20GSM%20evolution.md) ([EDGE](../Concepts/General/enhanced%20data%20rates%20for%20GSM%20evolution.md))
- [3G](../Concepts/Telecommunications/3G.md)
- H - [High-speed packet access (HSPA)](../Concepts/General/High-speed%20packet%20access.md)
- H+ - evolved [HSPA](../Concepts/General/High-speed%20packet%20access.md) ([HSPA](../Concepts/General/High-speed%20packet%20access.md)+)
- [4G](../Concepts/General/4G.md)
- [5G](../Concepts/General/5G.md)
## Do we still use the old standards?
- Modern phones attempt to maintain the [data rate](../Concepts/General/data%20rate.md) depending on the channel
- Higher standard requires a higher [SNR](../Concepts/General/signal%20to%20noise%20ratio.md) or [signal to interference ratio](../Concepts/General/signal%20to%20interference%20ratio.md)
- If channel condition is not good - [base station](../Concepts/General/Base%20station.md) may fall back on an older standard.
- [Resource Allocation](../Concepts/General/Resource%20Allocation.md) makes best use of what is available
## Duplexing and multiple access strategies
### Duplexing
Problem:
- Transmitted power = 30dBm
- Received power is -100dBm
Power difference is 130dB which is 10,000,000,000,000 times larger!
The transmit power will overwhelm the receive power ([self-interference](../Concepts/General/self-interference.md))
There is no [full duplex](../Concepts/General/full%20duplex.md) in commercial mobile [communications](../Concepts/General/Communications.md)!
It does exist in research (prototype).
## Half-Duplex Solution
- [Frequency Division Duplexing](../Concepts/General/Frequency%20Division%20Duplexing.md)
- [Time Division Duplexing](../Concepts/General/Time%20Division%20Duplexing.md)
>[!note] What do systems use in practice?
>Practical systems mainly implement [FDD](../Concepts/General/Frequency%20Division%20Duplexing.md) for a shorter delay - transmit and receive at the same time. No time delay in the system.
## Multiple Access
One direction that needs to be used by different users.
- [Frequency division multiple access](../Concepts/General/Frequency%20division%20multiple%20access.md)
- [Time division multiple access](../Concepts/General/Time%20division%20multiple%20access.md)
- [Code division multiple access](../Concepts/General/Code%20division%20multiple%20access.md)
- [Spatial division multiple access](../Concepts/General/Spatial%20division%20multiple%20access.md)
>[!tip] How to remember
>"T"-something means takes turns!
## Fundamental System Tradeoff: Error rate vs. Data rate
You can have fast transmission but everything is in error or very reliable but slow [data rate](../Concepts/General/data%20rate.md).
## Multiple access Strategies and Duplexing
The capacity is the same, because it doesn't matter how you cut the cake!
## Key Technologies
### Goals
1. High data rates
2. High energy efficiency
3. Ubiquitous wireless servive
### Key Technology
1. [Diversity](../Concepts/General/diversity%20scheme.md) (time, frequency, spatial, etc.)
2. [Channel coding](../Concepts/General/Channel%20coding.md) (error correction)
1. A CD - you can still play it with scratches which corrupts some bits
2. [Channel coding](../Concepts/General/Channel%20coding.md) creates robustness against error
1. TELE4653
3. Spread spectrum
4. [Orthogonal frequency division multiplexing](../Concepts/General/Orthogonal%20frequency%20division%20multiplexing.md)
1. Talk to Jinhong
5. [Multiple-input multiple-output](../Concepts/General/Multiple-input%20multiple-output.md)
6. Adaptive modulation
1. When the channel is good you transmit more bits
7. [Mutli-user diversity](../Spaces/University/TELE4652/MOCs/Mobile%20and%20Satellite%20Communications.md)
## Cellular Concepts
Phones are cell-phones not mobile phones!
Imagine you have a spectrum (billions of dollars)
10 MHz [forward channel](../Concepts/General/uplink.md) and 10 MHz [reverse channel](../Concepts/General/downlink.md) using [FDD](../Concepts/General/Frequency%20Division%20Duplexing.md)
### Early days
Longer distance, larger power $P_R\propto\frac{1}{d^2}$.
Power and spectrum are limited system resources
#### Advantages
- Good coverage
- Simple
#### Disadvantages
- Impossible to reuse the same frequency throughout
- Waste of transmit power
- Can only support limited users (70s - 12 supported calls over 1000 square miles)
### Cellular
A major breakthrough in solving the problem of spectral congestion and user capacity.
Offered a very high
No hardware changes, just play around with assignment.
[frequency reuse](../Concepts/General/frequency%20reuse.md)
[cell footprint](../Concepts/General/cell%20footprint.md)
[SIR and Capacity tradeoff](../Concepts/General/SIR%20and%20Capacity%20tradeoff.md)
## Issues associated with Cellular Structure
1. Frequency channel assignment
1. [Fixed channel assignment](../Concepts/General/Fixed%20channel%20assignment.md)
2. [Dynamic channel assignment](../Concepts/General/Dynamic%20channel%20assignment.md)
2. [Handoff](../Concepts/General/Handoff.md)
1. Switching from one cell to another.
2. Neighbouring cells use different frequencies
3. Power control
1. Minimises transmit power to lower interference to other students
2. Solving a form of multicell interference could constitute a PhD.
3. If you increase your transmit power you harm other [base stations](../Concepts/General/Base%20station.md).
4. If a [dynamic channel assignment](../Concepts/General/Dynamic%20channel%20assignment.md) is used, it increases the amount of [frequency reuse](../Concepts/General/frequency%20reuse.md)
4. More complicated methods to calculate capacity
1. Exploit statistical properties since users aren't using the system constantly.
## Traffic Issues
There is no perfect communication - we try to exploit statistics to get the best case.
1. Attempt rate or arrival rate
1. On average, how often will you make a phone call?
2. [Holding time](../Concepts/General/Holding%20time.md) or service time
3. Number of servers, C (number of simultaneous calls supported)
4. Treatment of blocked attempts (blocked calls, delayed calls)
1. A call might take time on christmas (delayed)
[Trunking theory](../Concepts/General/Trunking%20theory.md)
## Calculating Blocking probabilities
Given a certain number of [channels](../Concepts/RF%20Chip%20Design/channels.md) C and an amount of user traffic A (behaviours of the users - how often and how long for), what is the probability that a connection attempt is blocked.
High level feeling - impose assumption to simplify the maths.
Assume:
1. All users have the same behaviour in terms of making/talking on the phone
2. Traffic distribution
3. Handling of blocked calls - first come first serve
4. How channel assignment is done
[Traffic Intensity](../Concepts/General/Traffic%20Intensity.md)
[^slides 2]
## More Traffic Issues
1. Mobile can move from cell to cell (arrival means new call or new [handoff](../Concepts/General/Handoff.md), at different rates)
2. Drop call and blocked call are different (different GOS requirement)
3. Guard (reserved) channel scheme require different queueing models
1. New calls aren't allowed to use guard [channels](../Concepts/RF%20Chip%20Design/channels.md)
2. Only [handoff](../Concepts/General/Handoff.md) can use the guard [channels](../Concepts/RF%20Chip%20Design/channels.md)
## Improving capacity and quality
1. [Cell splitting](../Concepts/General/Cell%20splitting.md)
2. [Sectoring](../Concepts/General/Sectoring.md)
3. [Channel coding](../Concepts/General/Channel%20coding.md)
4. Modulation
5. [Diversity](../Concepts/General/diversity%20scheme.md)
Play with big N and hope that A reduces. Can also play with K (number of interferes)
## Traffic Issues Example
A city with area $1300km^2$ using cell radius 4km has 350 2-way traffic [channels](../Concepts/RF%20Chip%20Design/channels.md). The [path loss](../Concepts/General/Path%20loss.md) exponent is 4. Assuming that the hexagonal cell pattern is used, there are 6 co-channel cells in the first tier and an SIR of 17dB is required.
1. What is the smallest N possible?
$SIR = \frac{\sqrt[n]{3N}}{K} \rightarrow N = \frac{\left(K\times SIR\right)^n}{3} =\frac{\left(6\times 10^{1.7}\right)^4}{3} = 2725735729$
2. What will the answer in question 1 change if cells with radius 2km are used instead? Which system parameters have to be changed?
3. With 2 km-radius cells, what is the number of [channels](../Concepts/RF%20Chip%20Design/channels.md) per cell?
4. What is the [traffic intensity](../Concepts/General/Traffic%20Intensity.md) per cell and the maximum [traffic intensity](../Concepts/General/Traffic%20Intensity.md) for the whole system? (assume a GOS at 2%)
5. If each user makes a call every hour and talks for 3 minutes, how many users can the whole system support?
6. How many users can be served at any given time?
7. What happens to questions 1 6 if the required [SIR](../Concepts/General/signal%20to%20interference%20ratio.md) is lowered by % dB?
## Mobile Radio Propagation Models
### Overview of wireless [channel models](../Concepts/General/channel%20model.md)
Exploit EM waves for conveying information.
| Effect | Wireless | Wired |
|:---:|:---:|:---:|
|Time varying (Doppler)|$\checkmark$|$\bigtimes$|
|Waveguide|$\bigtimes$|$\checkmark$|
|Interference|$\checkmark$|$\bigtimes$ [^1]|
### Wireline
There is a wave guide.
Two pairs of cables - as long as these are separated, they should be fine (insulated).
Avoid interference!
### Wireless
You only collect a small portion of the transmit power (small received power)
Also uses a shared [medium](../Concepts/General/medium.md).
Increasing transmit power is not always the solution.
Performance is limited by the channel.
The channel puts fundamental limitations to the performance of wireless communications systems i.e. capacity ^[measured in bits/s/Hz] ^[this is different to [system capacity](../Concepts/General/system%20capacity.md) as "number of users"]
Radio channels are random and not easy to analyse.
We use a channel model to study:
1. System performance (e.g. bit error rate, capacity, [outage probability](../Concepts/General/outage%20probability.md))
2. Communication technology designs (e.g. equaliser, precoding, [beamforming](../Concepts/General/Beamforming.md))
[Channel models](../Concepts/General/channel%20model.md)
### 3-level Propagation model
#### Level 3: Path loss
[pathloss](../Concepts/General/Path%20loss.md)
#### Level 2: Shadowing
[Shadowing](../Concepts/General/Shadowing.md)
#### Level 1: Multipath Fading
[Multipath Fading](../Concepts/General/Multipath%20Fading.md)
## Assessments
[TELE4652 Homework 1](../Spaces/University/TELE4652/Homework%201/TELE4652%20Homework%201.md)
[TELE4652 Homework 2](../Spaces/University/TELE4652/Homework%202/TELE4652%20Homework%202.md)
## Labs
[TELE4652 Lab 1](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%201.md)
[TELE4652 Lab 2](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%202.md)
[TELE4652 Lab 3A](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%203A.md)
[TELE4652 Lab 3B](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%203B.md)
[TELE4652 Lab 4A](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%204A.md)
[TELE4652 Lab 4B](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%204B.md)
[TELE4652 Lab 5](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%205.md)
[TELE4652 Lab 6](../Spaces/University/TELE4652/Support%20Notes/TELE4652%20Lab%206.md)
## Finals
[TELE4652 Final Q1](../Spaces/University/TELE4652/Final/TELE4652%20Final%20Q1.md)
[TELE4652 Final Q2](../Spaces/University/TELE4652/Final/TELE4652%20Final%20Q2.md)
[TELE4652 Final Q3](../Spaces/University/TELE4652/Final/TELE4652%20Final%20Q3.md)
[TELE4652 Final Q4](../Spaces/University/TELE4652/Final/TELE4652%20Final%20Q4.md)
[TELE4652 Final Q5](../Spaces/University/TELE4652/Final/TELE4652%20Final%20Q5.md)
# References
1.
# Footnotes
[^1]: Cross talk can be avoided by separating cables.