Question

OFDM is also sometimes referred to as multicarrier modulation. In the context of OFDM, explain the difference between multicarrier and single-carrier transmission. You may find it useful to include diagrams as part of your explanation.

Full marks can be gained with an answer of fewer than 150 words

Answer 1

Difference between Single Carrier transmission and Multi carrier transmission

Single Carrier transmission	Multi carrier transmission
One radio frequency carrier is used to carry information	Multiple carrier signals at different frequencies are used
IFFT(Inverse Fast Fourier Transform) is not used at the transmitter	IFFT is used at the transmitter
Data rate is lower	Data rate is higher
Reduced peak on average power ratio of transmitted signal	high peak to average power ratio
Eg: Satellite communication systems	Wimax broad band

Answer 2

In the context of OFDM (Orthogonal Frequency Division Multiplexing), let's explain the difference between multicarrier and single-carrier transmission.

Single-Carrier Transmission:In single-carrier transmission, data is transmitted using a single continuous carrier wave. The entire data stream is modulated onto this single carrier, and the modulated signal is transmitted over the channel. This means that all the information is sent at once in a single frequency band.

Advantages of Single-Carrier Transmission:

Simplicity: Single-carrier modulation is straightforward to implement and requires less complex hardware.

Lower Peak-to-Average Power Ratio (PAPR): The signal's PAPR is generally lower in single-carrier systems, making it more power-efficient in some cases.

Disadvantages of Single-Carrier Transmission:

Inter-symbol Interference (ISI): In high-data-rate scenarios or in frequency-selective fading channels, ISI may occur, leading to a loss of data integrity and requiring sophisticated equalization techniques.

Inefficiency in Frequency-Selective Channels: Single-carrier systems may not efficiently utilize the available frequency bandwidth, especially in frequency-selective channels.

Multicarrier Transmission (OFDM):In multicarrier transmission (OFDM), the data stream is divided into multiple parallel substreams, each modulated onto a separate subcarrier. These subcarriers are closely spaced and orthogonal to each other, meaning they do not interfere with each other. By transmitting data in parallel over multiple subcarriers, OFDM effectively converts a frequency-selective channel into multiple frequency-flat subchannels.

Advantages of Multicarrier Transmission (OFDM):

Resilience to Frequency-Selective Fading: OFDM effectively mitigates the effects of frequency-selective fading, as each subcarrier experiences flat fading, and ISI is significantly reduced.

Efficient Spectrum Utilization: OFDM allows for efficient utilization of the available frequency spectrum, enabling higher data rates compared to single-carrier systems.

Robustness to Delay Spread: OFDM is robust against multipath delay spread, making it suitable for wireless communication in environments with significant reflections.

Disadvantages of Multicarrier Transmission (OFDM):

Higher PAPR: OFDM signals often have higher peak-to-average power ratios (PAPR), which may require additional power amplification and can cause power inefficiencies.

Complex Implementation: Implementing OFDM requires more complex signal processing and hardware compared to single-carrier systems.

Overall, the use of multicarrier modulation, such as OFDM, has become prevalent in many communication systems, including Wi-Fi, 4G, and 5G cellular networks, due to its ability to address the challenges posed by frequency-selective fading and efficiently utilize the available spectrum for high data-rate transmission.