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"