Machine-to-machine communication

Machine-to-machine communication, or M2M, is exactly as it sounds: two machines “communicating,” or exchanging data, without human interfacing or interaction. This includes serial connection, powerline connection (PLC), or wireless communications in the industrial Internet of Things (IoT). Switching over to wireless has made M2M communication much easier and enabled more applications to be connected.

As businesses have realized the value of M2M, it has taken on a new name: the Internet of Things (IoT). IoT and M2M have similar promises: to fundamentally change the way the world operates. Just like IoT, M2M allows virtually any sensor to communicate, which opens up the påossibility of systems monitoring themselves and automatically responding to changes in the environment, with a much reduced need for human involvement. M2M and IoT are almost synonymous—the exception is IoT (the newer term) typically refers to wireless communications, whereas M2M can refer to any two machines—wired or wireless—communicating with one another.

Traditionally, M2M focused on “industrial telematics,” which is a fancy way of explaining data transfer for some commercial benefit. But many original uses of M2M still stand today, like smart meters. Wireless M2M has been dominated by cellular since it came out in the mid-2000’s with 2G cell networks. Because of this, the cellular market has tried to brand M2M as an inherently cellular thing by offering M2M data plans. But cellular M2M is only one subsection of the market, and it shouldn’t be thought of as a cellular-only area.

How M2M Works

As previously stated, machine-to-machine communication makes the Internet of Things possible. According to Forbes, M2M is among the fastest-growing types of connected device technologies in the market right now, largely because M2M technologies can connect millions of devices within a single network. The range of connected devices includes anything from vending machines to medical equipment to vehicles to buildings. Virtually anything that houses sensor or control technology can be connected to some sort of wireless network.

This sounds complex, but the driving thought behind the idea is quite simple. Essentially, M2M networks are very similar to LAN or WAN networks, but are exclusively used to allow machines, sensors, and controls, to communicate. These devices feed information they collect back to other devices in the network. This process allows a human (or an intelligent control unit) to assess what is going on across the whole network and issue appropriate instructions to member devices.

M2M Applications

The possibilities in the realm of M2M can be seen in four major use cases, which we’ve detailed below:

1. MANUFACTURING

Every manufacturing environment—whether it’s food processing or general product manufacturing—relies on technology to ensure costs are managed properly and processes are executed efficiently. Automating manufacturing processes within such a fast-paced environment is expected to improve processes even more. In the manufacturing world, this could involve highly automated equipment maintenance and safety procedures.

For example, M2M tools allow business owners to be alerted on their smartphones when an important piece of equipment needs servicing, so they can address issues as quickly as they arise. Sophisticated networks of sensors connected to the Internet could even order replacement parts automatically.

2. HOME APPLIANCES

IoT already affects home appliance connectivity through platforms like Nest. However, M2M is expected to take home-based IoT to the next level. Manufacturers like LG and Samsung are already slowly unveiling smart home appliances to help ensure a higher quality of life for occupants.

For example, an M2M-capable washing machine could send alerts to the owners’ smart devices once it finishes washing or drying, and a smart refrigerator could automatically order groceries from Amazon once its inventory is depleted. There are many more examples of home automation that can potentially improve quality of life for residents, including systems that allow members of the household to remotely control HVAC systems using their mobile devices. In situations where a homeowner decides to leave work early, he or she could contact the home heating system before leaving work to make sure the temperature at home will be comfortable upon arrival.

3. HEALTHCARE DEVICE MANAGEMENT

One of the biggest opportunities for M2M technology is in the realm of health care. With M2M technology, hospitals can automate processes to ensure the highest levels of treatment. Using devices that can react faster than a human healthcare professional in an emergency situation make this possible. For instance, when a patient’s vital signs drop below normal, an M2M-connected life support device could automatically administer oxygen and additional care until a healthcare professional arrives on the scene. M2M also allows patients to be monitored in their own homes instead of in hospitals or care centers. For example, devices that track a frail or elderly person’s normal movements can detect when he or she has had a fall and alert a healthcare worker to the situation.

4. SMART UTILITY MANAGEMENT

In the new age of energy efficiency, automation will quickly become the new normal. As energy companies look for new ways to automate the metering process, M2M comes to the rescue, helping energy companies automatically gather energy consumption data, so they can accurately bill customers. Smart meters can track how much energy a household or business uses and automatically alert the energy company, which supplants sending out an employee to read the meter or requiring the customer to provide a reading. This is even more important as utilities move toward more dynamic pricing models, charging consumers more for energy usage during peak times.

A few key analysts predict that soon, every object or device will need to be able to connect to the cloud. This is a bold but seemingly accurate statement. As more consumers, users, and business owners demand deeper connectivity, technology will need to be continually equipped to meet the needs and challenges of tomorrow. This will empower a wide range of highly automated processes, from equipment repairs and firmware upgrades to system diagnostics, data retrieval, and analysis. Information will be delivered to users, engineers, data scientists, and key decision-makers in real time, and it will eliminate the need for guesswork.

The Value Of M2M

Growth in the M2M and IoT markets has been growing rapidly, and according to many reports, growth will continue. Strategy Analytics believes that low power, wide-area network (LPWAN) connections will grow from 11 million in 2014 to 5 billion in 2022. AndIDC says the market for worldwide IoT solutions will go from $1.9 trillion in 2013 to $7.1 trillion in 2020.

Many big cell operators, like AT&T and Verizon, see this potential and are rolling out their own M2M platforms. Intel, PTC, and Wipro are are all marketing heavily in M2M and working to take advantage of this major industry growth spurt. But there is still a great opportunity for new technology companies to engage in highly automated solutions to help streamline processes in nearly any type of industry. We’re certain we’ll see a huge influx of companies who begin to innovate in this area in the next five years.

However, as the cost of M2M communication continues to decrease, companies must determine how they will create value for businesses and customers. In our mind, the opportunity and value for M2M doesn’t lie in the more traditional layers of the communication world. Cell carriers and hardware manufacturers, for example, are beginning to look into full-stack offerings that enable M2M and IoT product development. We strongly believe value lies in the application side of things, and the growth in this industry will be driven by smart applications from this point forward.

Conclusion

Companies shouldn’t think about IoT or M2M for the sake of IoT or M2M. Instead, they should focus on optimizing their business models or providing new value for their customers. For example, if you’re a logistics company like FedEx or UPS, you have obvious choices for automated logistics decisions made by machines. But if you’re a retailer, the transition to automation may not be as obvious. It’s one thing to think of a “cool” automated process—say, creating advertising that is automatically tied to a specific customer through the use of M2M technology—but before you move forward with the process, you have to consider the value you’re getting out of it. How much does it cost to implement? Will it actually target the right audience? Will it be effective?
Any company considering a move into the IoT space needs to understand what its business model is, how it will make money, and how it will provide value for customers or internal processes.

LTE UE Procedure

i) UE is Off

ii) Power On UE

iii) < Frequency Search >

iv) < Cell Search > : Normally a UE would find multiple cells in this process

v) < Cell Selection >

vi) MIB decoding

vii) SIB deconding

viii) < Initial RACH Process >

ix) < Registration/Authentication/Attach>

x) <Default EPS Bearer Setup >

xi) Now UE is in IDLE Mode

xi) <(If the current cell become weak or UE moves to another cell regisn) Cell Reselection>

xii) <(When Paging message comes or User make a call) RACH Process>

xiii) < Setup Dedicated EPS Bearer >

xiv) Receive data

xv) Transmit data

xvi)  (If UE power is percieved too weak by the network) Network send TPC command to increase UE Tx Power

xvii) (If UE power is percieved too strong by the network) Network send TPC command to decrease UE Tx Power

xviii) < (If UE moves to another cell region) Network and UE perform Handover procedure >

xix) User stop call and UE gets into IDLE mode

LTE Cell Search - Synchronization Procedure

UE searches in all centre frequencies

Primary synchronization Signal(PSS) 

• achieve subframe, slot and symbol synchronisation in the time domain 
• identify the center of the channel bandwidth in the frequency domain 
• Physical Layer ID (N2CellID)

PSS is Zadoff-Chu sequence which is CAZAC.

Transmitted on last symbol of slot 0 and 10 for FDD, third symbol of slots 2 and 12 for TDD.

Secondary Synchronization signal(SSS)

• gives cell ID group(N1CellID)
• frame timing
• CP length
• TDD/FDD

SSS is constructed using two interleaved maximum length sequences.

Transmitted on second last symbol of slot 0 and 10 in FDD, last symbol of slots 1 and 11 in TDD.

DSP Code Optimization Techniques for Speed

Code can be optimized for Speed or memory.
Here I am discussing the methods for optimization for speed

Optimization can can be done at different levels

Design level

At the highest level, the design may be optimized to make best use of the available resources. The implementation of this design will benefit from a good choice of efficient algorithms and the implementation of these algorithms will benefit from being written well. The architectural design of a system overwhelmingly affects its performance. The choice of algorithm affects efficiency more than any other item of the design and, since the choice of algorithm usually is the first thing that must be decided, arguments against early or "premature optimization" may be hard to justify.

In some cases, however, optimization relies on using more elaborate algorithms, making use of "special cases" and special "tricks" and performing complex trade-offs. A "fully optimized" program might be more difficult to comprehend and hence may contain more faults than unoptimized versions.

Source code level

Avoiding poor quality coding can also improve performance, by avoiding obvious "slowdowns". After that, however, some optimizations are possible that actually decrease maintainability. Some, but not all, optimizations can nowadays be performed by optimizing compilers.

Build level

Between the source and compile level, directives and build flags can be used to tune performance options in the source code and compiler respectively, such as using preprocessor defines to disable unneeded software features, or optimizing for specific processor models or hardware capabilities. Source-based software distribution systems such as BSD's Ports and Gentoo's Portage can take advantage of this form of optimization.

Compile level

Use of an optimizing compiler tends to ensure that the executable program is optimized at least as much as the compiler can predict.

Using Intrisics 

Intrisics are functions equivalent to assembly instructions - one to one or one to many mapping.

These can be used in the code like a function.

Assembly level

At the lowest level, writing code using an assembly language, designed for a particular hardware platform can produce the most efficient and compact code if the programmer takes advantage of the full repertoire of machine instructions. Many operating systems used on embedded systems have been traditionally written in assembler code for this reason. Programs (other than very small programs) are seldom written from start to finish in assembly due to the time and cost involved. Most are compiled down from a high level language to assembly and hand optimized from there. When efficiency and size are less important large parts may be written in a high-level language.

With more modern optimizing compilers and the greater complexity of recent CPUs, it is harder to write more efficient code than what the compiler generates, and few projects need this "ultimate" optimization step.

Much code written today is intended to run on as many machines as possible. As a consequence, programmers and compilers don't always take advantage of the more efficient instructions provided by newer CPUs or quirks of older models. Additionally, assembly code tuned for a particular processor without using such instructions might still be suboptimal on a different processor, expecting a different tuning of the code.

Run time

Just-in-time compilers and assembler programmers may be able to perform run time optimization exceeding the capability of static compilers by dynamically adjusting parameters according to the actual input or other factors.

Self-modifying code can alter itself in response to run time conditions in order to optimize code.

Some CPU designs can perform some optimizations at runtime. Some examples include Out-of-order execution, Instruction pipelines, and Branch predictors. Compilers can help the program take advantage of these CPU features, for example through instruction scheduling.

Why Special Subframe is needed in LTE

As the single frequency block is shared in time domain between UL and DL the transmission in TDD is not continuous. All UL transmission need to be on hold while any downlink resource it is used and the other way around. 
Switching between transmission directions has a small hardware delay (for both UE and NodeB) and needs to be compensated. To control the switching between the UL and DL a guard period GP is allocated which compensates for the maximum propagation delay of interfering components.


Within a radio frame, the transmission direction changes several times between downlink and uplink. 

In special subframe DL to UL switching happens.
Special subframe includes DL,UL and a guard period.



Due to the different signal transit times between the eNodeB and the various mobile stations, a timing advance mechanism involving a time gap called “guard period” is needed when the transmission direction switches from downlink to uplink. However, no guard period is needed when the transmission direction switches from uplink to downlink. 


In the uplink,as shown in above figure the greater the distance between the eNodeB and the mobile station, the earlier the mobile station must start transmitting. This helps ensure that all signals reach the eNodeB in a frame-synchronous manner. When switching from downlink to uplink, a guard period is inserted between the DwPTS and UpPTS field in each special subframe. The duration of the guard period is configured by the network, based on the cell size. The maximum possible guard period length of ten OFDM symbols allows cell sizes with a radius of 100 km. 


When switching from uplink to downlink there is no need for a guard period, since the uplink signals all arrive at the eNodeB in a frame-synchronous fashion - thanks to the timing advance mechanism - and the downlink data is also transmitted in the form of a frame-synchronous OFDMA signal.


DwPTS : Downlink Pilot Time Slot
UpPTS :  Uplink Pilot Time Slot

Why Special Subframe is required in LTE?

In LTE Frame Type 2 (TD-LTE) there is a special sub-frame when switching from DL to UL but there is no special sub-frame or gap when switching from UL to DL. 

Different TDD modes

To understand this, it is important to know why a transmission gap is required when switching from DL to UL. The special sub-frame is made up of DwPTS, GP and UpPTS and all of these have configurable lengths while the sum of the lengths has to be 1 ms i.e. the length of the sub-frame. Now consider, the format 1, where the GP (guard period or TTG in WiMAX) is 4 symbols long which equates to 285 us approx. Consider a UE-A at a distance of 10 km from the eNB and UE-B at 50 km from the eNB. The time it takes the RF signals to reach the UE-A and UE-B will be

Time for UE-A = distance/velocity of light = 10000/3x10^8 = 33.3 us

Time for UE-B = distance/velocity of light = 45000/3x10^8 = 150 us

This means that after the eNB has transmitted the last symbol of DL data and it starts the GP, the last symbol will be received at UE-A after 33.3 us and at UE-B after 150 us. Now, every UE takes a small amount of time to switch from Rx to Tx mode and lets assume this switching period to be 50 us (it should be lesser for LTE UEs but this is just an assumption). So, the UE-A will start its switching period and will start transmitting after 33.5 + 50 = 83.5 us and it will take another 33.5 us to reach the eNB. This makes the total Round Trip Time for UE-A to be equal to 33.5 +50 + 33.5 = 117 us. Now we know that the GP at eNB is set 285 us so that means that the UE-A will be able to transmit the UL data within the GP. In actual practice, all the UEs know their Timing Advance from the eNB so the UE-A would wait that much amount before transmitting so that the UL data reaches the eNB at exactly the end of GP.

However, lets do the same analysis for UE-B. The total round trip time for UE-B would be 150 + 50 + 150 = 350 us which is greater than the GP (285 us) so, the UE-B would not be able to reach the first uplink symbol. Because of this, the GP is supposed to determine the maximum cell radius for a TDD system.

If there hadn't been a GAP or TTG (as in WiMAX) between the DL and UL transmission, these Over-The-Air timing delays and the switching period could not be compensated so we need to add a transmission gap when switching from DL to UL.

Now, lets consider the UL to DL switching. We will only consider UE-A for this example as UE-B has been proven beyond the cell range. The UE-A will transmit the last UL symbol and then start switching from Tx to Rx mode. The last UL symbol will reach the eNB after 33.5 us and the eNB would switch to Tx after receiving the last UL symbol. It will transmit the next DL symbol which will reach the UE-A after another 33.5 us and thus the UE-A will have a total of 33.5 + 33.5 = 67 us of time to switch from Tx to Rx mode without any presence of any RTG. So, while switching from UL to DL, a RTG or GP is not really required as the system already gets a virtual GP due to OTA delays.

There can be a query about the UEs that are very close to the eNB as they would have a very small Over-The-Air delay so it might not get enough time to switch to Rx mode. There can be two possible solutions for that

- In LTE, there is a 1 ms TTI so if the UE is too close to the eNB that it would not be able to switch to Rx mode in time, the eNB can allocate the DL resources in the next DL sub-frame so the UE will have 1 ms to make the switch. In WiMAX, this would not have been possible as it has 5 ms TTI and in case of No RTG, the UEs closer to WiMAX BTS would have to be scehduled in the next frame adding another 5 ms to the latency plane.

- Secondly, the UE switching from Rx to Tx and vice versa should now be extensively reduced. The 50 us limitation was there in beceem chipsets around 4 years back while I think that beceem and intel had made chipsets with switching periods of less than 20 us last year. SO, LTE UEs should have a much lower switching times.

3GPP LTE : Valid numbers of allocated Resource blocks in UL (Uplink)

Total number of allocated resource block for a user can only be any of these.

0
1
2
3
4
5
6
8
9
10
12
15
16
18
20
24
25
27
30
32
36
40
45
48
50
54
60
64
72
75
80
81
90
96
100

Condition for valid number 2^a * 3^b *  5^c
a,b,c = 0,1,2,....

3GPP LTE : Dynamic Scheduling, Persistent Scheduling and Semi Persistent Scheduling

Dynamic Scheduling

In a subframe in physical layer the first OFDM symbol of each subframe consists of CFI information. CFI information basically tells you the number of OFDM symbols used by PDCCH. The PDCCH has DCI information that lets you decode the data from the PDSCH. In case you forgot, PDSCH has all the user data pertaining to the UE's. Now when a UE is downloading a set of files, say from the internet, each and every subframe has the PCFICH and PDCCH data in the first 3-4 OFDM symbols. This is essential when the data is robust or adaptive in nature, especially when it is web data. So it is essential that you send the control information for each subframe along with it. This kind of Scheduling is known as Dynamic Scheduling.

The advantage of Dynamic Scheduling is basically the flexibility to alter the size of data in each subframe. You can push more data in one SF, less on another. 

Persistent Scheduling 

Now consider a case where the amount of data expected is less and occurs in a fixed time interval. Yes, I'm talking about something like VoLTE (Voice over LTE). Voice data is in the form of small packets and it comes in a regular interval, which is network dependent. In such cases, sending control information in each and every subframe plays a vital role in the effective utilization of bandwidth. Thus, we use something called as Persistent Scheduling, where the control information sent across a SF is retained for every nth SF coming after it, until notified. This scheme drastically reduces the overhead.

Semi Persistent Scheduling

Now note the point that when you have a NACK for any of the DL data, the retransmission has to contain some extra information. ( Probably to indicate retransmission, SF number so on). So your retransmissions cant be pushed along with the Persistent Scheduled Time interval. In other words, you have to explicitly put the header info for retransmission SF's. Thus, Persistent Scheduling is rarely used, instead this new scheduling scheme known as Semi Persistent Scheduling is used.

Semi Persistent Scheduling Example

The time interval for SPS is informed by the RRC. The termination of SPS/alteration of time interval is also RRC triggered.

    

In VoIP services, the voice data is encoded using a codec and sent. At times, the network might have to change the codec(maybe for internal reasons, or say clarity etc). When you change the codec, the amount of data sent per Radio Frame might be different. As a result, you might have to increase the SPS interval.

In the diagram above, also note one thing. Once SPS is triggered, every nth SF is first checked for PDCCH data. This is because, PDCCH signals always have a higher priority. So just because you initiated SPS, it doesnt mean that it will continue till you tell it to stop. It will always give a higher priority for PDCCH data in that particular SF. An example for this would be downloading a webpage along with a voice call. Here, you might need PDCCH data to decode the user data.

LTE Physical Layer Simulation in Scilab. Please join to develop

Hi

I have four years of experience in working in 3GPP LTE physical layer.
Now I'm planning of making LTE Physical layer simulation in Scilab to help the students.
If you are interested in this project please contact me.

Regards
Ashok

LTE Resource Grid Visualization

Nice website to see LTE subframe structure for different configurations

http://paul.wad.homepage.dk/LTE/lte_resource_grid.html

How to Find the nearest power of 2

/* returns greatest power of 2 less than or equal to x, branch-free */

int
flp2(int x)
{
    x = x | (x>>1);
    x = x | (x>>2);
    x = x | (x>>4);
    x = x | (x>>8);
    x = x | (x>>16);
    return x - (x>>1);
}

It's entertaining to study it and see how it works. I think the only way for you to know for sure which of the solutions you see will be optimal for your situation is to use all of them in a text fixture and profile it and see which is most efficient for your purpose.

Being branch-free, this one is likely to be quite good performance-wise relative to some others, but you should test it directly to be sure.

If you want the least power of two greater than or equal to X, you can use a slightly different solution:

unsigned
clp2(unsigned x)
{
    x = x -1;
    x = x | (x >> 1);
    x = x | (x >> 2);
    x = x | (x >> 4);
    x = x | (x >> 8);
    x = x | (x >> 16);
    return x + 1;
}

DAI (Downlink Assignment Index) in LTE

The DL assignment carries a Downlink Assignment Index (DAI) indicating how many assignments the UE should have received so far within the current bundling window. If the UE detects that the DAI differs from the number of correctly received DL assignments, it does not send any HARQ feedback and the eNB can detect this. However, the eNB cannot know which of the transmissions was missed, and thus the whole bundle has to be retransmitted.

RSSI,SINR,RSRP and RSRQ in LTE

RSSI,SINR,RSRSP and RSRQ : These are  the basic measurement quantities used in LTE.
RSSI - Received Signal Strength Indicator
SINR - Signal to Interference & Noise Ratio
RSRP - Reference Signal Received Power
RSRQ - Reference Signal Received Quality

RSRP is a measure of signal strength. It is of most importance as it used by the UE for the cell selection and reselection process and is reported to the network to aid in the handover procedure. For those used to working in UMTS WCDMA it is equivalent to CPICH RSCP.

The 3GPP spec description is "The RSRP (Reference Signal Received Power) is determined for a considered cell as the linear average over the power contributions (Watts) of the resource elements that carry cell specific Reference Signals within the considered measurement frequency bandwidth."

In simple terms the Reference Signal (RS) is mapped to Resource Elements (RE). This mapping follows a specific pattern (see below). So at any point in time the UE will measure all the REs that carry the RS and average the measurements to obtain an RSRP reading.

RSRQ is a measure of signal quality. It is measured by the UE and reported back to the network to aid in the handover procedure. For those used to working in UMTS WCDMA is it equivalent to CPICH Ec/N0. Unlike UTMS WCDMA though it is not used for the process of cell selection and reselection (at least in the Rel08 version of the specs).

The 3GPP spec description is "RSRQ (Reference Signal Received Quality) is defined as the ratio: N×RSRP/(E -UTRA carrier RSSI) where N is the number of Resource Blocks of the E-UTRA carrier RSSI measurement bandwidth."

The new term that appears here is RSSI (Received Signal Strength Indicator). RSSI is effectively a measurement of all of the power contained in the applicable spectrum (1.4, 3, 5, 10, 15 or 20MHz). This could be signals, control channels, data channels, adjacent cell power, background noise, everything. As RSSI applies to the whole spectrum we need to multiple the RSRP measurement by N (the number of resource blocks) which effectively applies the RSRP measurement across the whole spectrum and allows us to compare the two.

Finally SINR is a measure of signal quality as well. Unlike RSRQ, it is not defined in the 3GPP specs but defined by the UE vendor. It is not reported to the network. SINR is used a lot by operators, and the LTE industry in general, as it better quantifies the relationship between RF conditions and throughput. UEs typically use SINR to calculate the CQI (Channel Quality Indicator) they report to the network.

The components of the SINR calculation can be defined as:

S: indicates the power of measured usable signals. Reference signals (RS) and physical downlink shared channels (PDSCHs) are mainly involved

I: indicates the power of measured signals or channel interference signals from other cells in the current system

N: indicates background noise, which is related to measurement bandwidths and receiver noise coefficients

LTE Uplink Physical Layer

Here is a brief description of LTE Uplink Physical Layer


LTE uplink Consists of

• PUSCH
• PUCCH
• PRACH
• SRS

PUSCH (Physical Uplink Shared Channel)


The physical uplink shared channel is used to transmit the uplink shared channel (UL-SCH) and L1 and L2 control information. The UL-SCH is the transport channel used for transmitting uplink data (a transport block). L1 and L2 control signalling can carry the following type of information: HARQ acknowledgements for received DL-SCH blocks, channel quality reports and scheduling requests. It uses SC-FDMA in physical layer

The processing blocks of PUSCH transmitter side is in the figure below.

Processing blocks at PUSCH receive, i.e, at eNodeB is in the figure below

More Details will be added soon based on the requirement..

Or you may refer :
http://www.steepestascent.com/content/mediaassets/html/LTE/Help/PUSCH.html

Please feel free to contact me if you need any details regarding LTE uplink. I will be happy share the knowledge I have.

LTE - Long Term Evolution

LTE, an initialism of long-term evolution, marketed as 4G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements.^[1][2] The standard is developed by the 3GPP (3rd Generation Partnership Project) and is specified in its Release 8 document series, with minor enhancements described in Release 9.

Although marketed as a 4G wireless service, LTE as specified in the 3GPP Release 8 and 9 document series does not satisfy the technical requirements the 3GPP consortium has adopted for its new standard generation, and which were originally set forth by the ITU-Rorganization in its IMT-Advanced specification. However, due to marketing pressures and the significant advancements that WIMAX,HSPA+ and LTE bring to the original 3G technologies, ITU later decided that LTE together with the aforementioned technologies can be called 4G technologies. ^[6] The LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced.^[7] And to differentiate LTE-Advanced and WiMAX-Advanced from current 4G technologies, ITU has defined them as "True 4G"

Cyclic Prefix (CP)

Cyclic Prefix (CP)

In telecommunications, the term cyclic prefix refers to the prefixing of a symbol with a repetition of the end. Although the receiver is typically configured to discard the cyclic prefix samples, the cyclic prefix serves two purposes.

• As a guard interval, it eliminates the intersymbol interference from the previous symbol.
• As a repetition of the end of the symbol, it allows the linear convolution of a frequency-selective multipath channel to be modelled as circular convolution, which in turn may be transformed to the frequency domain using a discrete Fourier transform. This approach allows for simple frequency-domain processing, such as channel estimation and equalization.

The intersymbolic interference is almost completely eliminated by introducing a guard time for a each OFDM symbol. The guard time is chosen larger than the expected delay spread such that multipath components from one symbol cannot interfere with the next symbol. This guard time could be no signal at all but the problem of intercarrier interference (ICI) would arise. Then, the OFDM symbol is cyclically extended in the guard time. Using this method, the delay replicas of the OFDM symbol always have an integer number of cycles within the FFT interval, as long as the delay is smaller than the guard time. Multipath signals with delays smaller than the guard time cannot cause ICI.

In order for the cyclic prefix to be effective (i.e. to serve its aforementioned objectives), the length of the cyclic prefix must be at least equal to the length of the multipath channel. Although the concept of cyclic prefix has been traditionally associated with OFDM systems, the cyclic prefix is now also used in single carrier systems to improve the robustness to multipath. 

LTE Bandwidth/Resource Configuration (for normal CP – 7 OFDM symbols)

Channel Bandwidth [MHz]	1.4	3	5	10	15	20
Number of resource blocks (N_RB)	6	15	25	50	75	100
Number of occupied subcariers	72	180	300	600	900	1200
IDFT(Tx)/DFT(Rx) size	128	256	512	1024	1536	2048
Sample rate [MHz]	1.92	3.84	7.68	15.36	23.04	30.72
Samples per slot	960	1920	3840	7680	11520	15360