![]() Receiver: It is an integrated RF hardware containing low noise amplifier (LNA), mixer for demodulation ,and ADC for converting analog baseband signal to digital domain for digital signal processing. Its main job is to up-shift baseband signal to RF signal and increases RF output power for transmission. Transmitter: It is an integrated RF hardware containing DAC for generating analog baseband signal, mixer for modulation, and power amplifier for over the air transmission. ![]() The main RF system design criteria is to minimize path loss and maximize power transfer using lumped matching network. Simplified Wireless Communication Block Diagram RF reception: A RF signal is picked up by the antenna and downshifted to low bandwidth (DC like) signal by a radio receiver. ![]() RF Transmission: A RF signal is created by upshifting a low bandwidth (DC like) signal to radio frequency by a radio transmitter. RF system is responsible for transmission and reception of wireless signals. Note: QPSK is a special type of 4-QAM where resultant signal has equal amplitude with varying phase.ĭemodulation is analogous to decoding a RF signal which involves removing carrier frequency component from the RF signal leaving the baseband signal behind for further processing. Quadrature Phase shift Keying (QPSK): It's a 2 bit modulation technique with 4 unique symbols, 00, 01, 10, 11 are represented by phase change (45,135, 225, or 315 degrees) of the carrier signal using I and Q components in quadrature amplitude modulation (QAM). This technique increases spectral efficiency (i.e more bits/symbol transmitted per fixed channel bandwidth). This is very clever and powerful because by varying amplitude and phase relationships of I & Q carriers, a range of unique symbols can be created resulting in an increase of bits/symbol Hence higher data throughput is achieved. Quadrature Amplitude modulation (QAM): a base band signal is encoded by summing two carrier signals 90 degrees out of phase (i.e I & Q components) resulting a single signal that is controlled by phase and amplitude variation of two I/Q carriers.ĭigital symbols are reconstructed by combination of amplitude and phase relationship of I & Q component. Phase Shift keying: 1 bit symbol binary signal modulation scheme where 1 and 0 is represented by change RF carrier signal phase relationship. It's is used to encode digital base band signal (i.e binary bits 0 and 1) onto a of RF carrier signal for short to mid range transmission with high data bandwidth such as large file download and video streaming.Īmplitude Shift Keying: 1 bit binary signal modulation scheme where 1 and 0 is represented by turning on and off RF carrier transmission.įrequency Shift Keying: 1 bit binary signal modulation scheme where 1 and 0 is represented by change RF carrier signal from high to low frequency. It's is used to encode analog baseband signal onto a RF carrier signal for long range transmission with low data bandwidth such as voice, small data packets.Īmplitude Modulation (AM): analog baseband signal is encoded on a RF carrier signal in the form of varying RF carrier signal amplitude.įrequency Modulation (FM) analog baseband signal is encoded on a RF carrier signal in the form of varying RF carrier signal frequency In the context of RF, one can think it in two ways:Įncoding a baseband message on a carrier frequency signal.įrequency shift the baseband signal to radio frequency signal. Modulation: Modulation means encoding a message. IQ signals is the building block of modern digital modulation and demodulation scheme. Quadrature I/Q Components: two components I (in phase signal) and Q (out of phase signal) are 90 degrees out of phase. ![]() Quadrature: Orthogonal relationship (i.e 90 degrees) between two vectors. Improved selectivity: easier filter design with sharper rolloff can be constructed at lower frequencies. Two main reasons for using low BW baseband signal are:Ĭome within sampling range of ADC/DAC: sampling rate are limited on ADC/DAC mixed signal hardware which is needed for pre/post digital signal processing. It's a low bandwidth analog signal containing data the such as voice and data typically found after downconverting from RF to DC before analog to digital converter (ADC) in radio receiver or right after digital to analog converter (DAC) in radio transmitter. The reason is that due to miniaturization of consumer electronics, high RF carrier signal is needed for efficient electromagnetic radiation using small antenna in transmission and reception of wireless network. It's a high frequency signal that "carries" the lower bandwidth of "real" information signal such voice and data In modern cellular standard LTE, the low band roughly starts at 600 MHz and extends to 6000 MHz (refer ) B46 is the last LTE band in frequency. A signal frequency with greater than 300 MHz is considered RF. ![]()
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