# Daily Report day 4 ::: success 23/07/2021 ::: ## 1. Aspects : Baseband Technology (Basic Principles of OFDM & OFDMA) :::info ### A. Introduction OFDM OFDM is a multiplexing technique that divides the available bandwidth into multiple orthogonal sub-carriers. Each sub-carrier can be modulated independently and carries different information. ::: :::info ### B. Bandwidth Efficiency ![](https://i.ibb.co/cb59y3G/2021-07-23-08h42-30.png) Multi-carrier method, which is to divide the wide bandwidth into a narrow spectrum (sub-carrier) and overlap each other. The sub-carriers are orthogonal to each other, so there is no interference. Orthogonality between sub-carriers obtained by IFFT process ::: :::info ### C. FDM vs OFDM ![](https://i.ibb.co/JcYDdxG/2021-07-23-08h45-15.png) FDM stands for Frequency Division Multiplexing. OFDM stands for Orthogonal Frequency Division Multiplexing. In FDM, Bandwidth(B) is committed to the different sources. In OFDM, Single data source attaches all the sub-channels. Applications of FDM are in radio and satellite communication. Applications of OFDM are in LTE technologies and broadband internet. ::: :::info ### D. Characteristics #### 1. Resistant to Fading ![](https://i.ibb.co/pnxmyGj/2021-07-23-08h49-10.png) Due to the width of the bandwidth used and the muti- path effect that occurs on the channel, the signal will experience a frequency selective fading effect. OFDM uses many sub-carriers with narrow bandwidth (smaller than coherence bandwidth), then each sub-carrier will only experience at fading, This reduces the complexity of the equalization process required on the receiver to compensate for the flat fading. ![](https://i.ibb.co/HND9rJV/2021-07-23-08h51-19.png) #### 2. Supports Various Operating Modes - Adaptive Modulation. - Adaptive Coding. - MIMO. - Duplex Mode. #### 3. Make It Easier to Sync Frequency and Time Using CP tours and preamble information on OFDM symbols makes it easy to synchronize frequency and time. #### 4. Simplify Channel Equalization Data processing features in frequency domains in THEDM system can simplify the process of estimating and equalizing data to remove influence from channels. ::: :::info ### E. Multi-Carrier Modulation on OFDM Ofdm s(t) modulated signals on time domains can be expressed with the following equation: ![](https://i.ibb.co/fNs4NBH/2021-07-23-08h57-37.png) Multicarrier data stream: ![](https://i.ibb.co/28dPRyt/2021-07-23-08h58-16.png) #### Transmitter and Receiver Multi-carrier modulation can be formed using Inverse Fast Fourier Transform (IFFT). ![](https://i.ibb.co/723dFBN/2021-07-23-09h00-40.png) OFDM Transmitter using IFFT: ![](https://i.ibb.co/fFqm22y/2021-07-23-09h02-08.png) OFDM Receiver using FFT: ![](https://i.ibb.co/smYvdhk/2021-07-23-09h04-35.png) ::: :::info ### F. Cyclic Prefix (CP) CP function is to maintain the orthogonality of ofdm signal so as to avoid the effect of Inter Carrier Interference (ICI), so that the minimum length of CP (TG period) should be greater than the delay of the channel response. The longer the CP period, the more resistant the signal will be to the multi-path effect. However, as CP lengthens the symbol, the longer CP can lower the SNR and signal efficiency. The decrease in SNR that occurs (SNRloss) can be defined as equation: ![](https://i.ibb.co/wJv1NSb/2021-07-23-10h21-11.png) The nature the cycle symbol with CP: ![](https://i.ibb.co/Kjd9SxH/2021-07-23-10h23-10.png) ::: :::info ### G. Symbol OFDM OFDM Transmitter: ![](https://i.ibb.co/6sBWjGj/2021-07-23-10h25-38.png) OFDM Receiver: ![](https://i.ibb.co/GnXG5b8/2021-07-23-10h26-45.png) ::: :::info ### H. Frame Structure OFDM Uplink Frame Structure in Time Domain: ![](https://i.ibb.co/gykTpsw/2021-07-23-10h39-11.png) OFDM Downlink Frame Structure in Time Domain: ![](https://i.ibb.co/xmQvbZ4/2021-07-23-10h40-11.png) In the OFDM system, the arrangement of several OFDM symbols forms a single OFDM Frame. In general, there are two types of frames, namely Uplink Frame OFDM and Downlink Frame OFDM. Uplink is a communication line from the Subscriber Station (SS) to the Base Station (BS). On the other hand, Downlink is a communication path from BS to SS. ::: :::info ### I. Code-Rate Code-rate is the information rate of the convolution code used in the error coding process. The value of the code-rate states how much of the useful information part of the amount of data sent. The value of 2/3 means that 2/3 of the data is useful, while the other 1/3 is redundancy. Determining the code-rate value considers the trade-off between error coding performance and bit rate. The greater the code rate, the greater the bit rate. However, error coding performance will get worse. Vice versa. An example of a code-rate that is usually determined by the standard is: 1/2. 2/3, 3/4, 5/6, 7/8. ::: :::info ### J. OFDMA Increasing system flexibility by multiplexing multiple users onto the same subcarriers. Efficient trunking of many low-rate users onto a shared channel. Enable per-user frequency hopping to mitigate the effects of narrowband fading. ![](https://i.ibb.co/ccYMF9C/2021-07-23-10h43-42.png) ::: :::info ### K. Modulation Modulation is the process of changing a periodic wave with a certain frequency in order to be able to carry information. The modulation-demodulation process is also known as Mapper-Demapper, which is the mapping of binary samples to complex number samples and vice versa (bit symbol). #### BPSK modulation Binary Phase Shift Keying (BPSK) is one type of Phase Shift Keying (PSK) modulation, information is stored in the form of a carrier signal phase shift. Signals are represented in 2 possible values. Signal '1' is represented by giving the carrier signal phase shift of 0o (the carrier signal phase is not shifted). #### QPSK modulation Quadrature Phase Shift Keying (QPSK) is a type of Phase Shift Keying (PSK) modulation. The information signal is stored in the phase shift parameter of the carrier signal. The signal is represented in one of 4 possible values for the phase shift of the carrier signal. #### 16-QAM Modulation Quadrature Amplitude Modulation (QAM) modulation technique is a combination of Phase Shift Keying Modulation (PSK) with Amplitude Modulation (AM). ::: :::info ### L. Demodulation Demodulation is the process of returning the bit value of the modulated signal y which consists of Real (I) and Imaginary (Q) components received. #### BPSK Demodulation The function of BPSK demodulation is to determine the value of one bit b0 of the received input signal y. #### QPSK Demodulation The QPSK demodulation mechanism is similar to BPSK, only that there are more constellation areas and the position of symbols on the constellation diagram depends on the value of b1b0. #### 16-QAM Demodulation There are 4 partitions of the constellation diagram. The bit in the modulation is defined as b3b2b1b0 with the Most Significant Bit (MSB) is b3. ::: :::info ### M. Single-Carrier (SC) FDMA * Special case of DFT-spread OFDMA with contiguous sub-carrier mapping * Used in Evolved UTRA uplink * Resulting spectrum becomes continuous – Single-Carrier - All N input symbols are spread over all N subcarriers - All N subcarriers are modulated with a weighted sum of all N input symbols - The DFT/IDFT pair in the transmitter cancel each other out retaining the time domain symbols with a shorter symbol (chip) rate. SC-FDMA block diagram: ![](https://i.ibb.co/RHjM4vX/2021-07-23-10h56-17.png) ::: ## 2. Summary :::info OFDM is a multiplexing technique that divides the available bandwidth into multiple orthogonal sub-carriers. Each sub-carrier can be modulated independently and carries different information. OFDMA is essentially a type of OFDM for multiple users. It allocates in both the time domain and the frequency domain, allowing for multiple users—even those with widely varying use patterns or data loads. Modulation is the process of changing a periodic wave with a certain frequency in order to be able to carry information. Demodulation is the process of returning the bit value of the modulated signal y which consists of Real (I) and Imaginary (Q) components received. The modulation-demodulation process is also known as Mapper-Demapper, which is the mapping of binary samples to complex number samples and vice versa (bit symbol). ::: ## 3. Comment One of the baseband technologies used in 5G o-ran is OFDM and OFDMA. It is a form of digital modulation and demodulation. --- # <center>Discussion with Team</center> --