SM Spatial Modulation

Last updated on Jul 3, 2023

Spatial Modulation (SM) is a transmission technique used in wireless communication systems to increase the data rate and spectral efficiency. It takes advantage of multiple antennas at the transmitter and receiver to simultaneously transmit different streams of data using the spatial dimensions. SM combines the benefits of both multiple-input multiple-output (MIMO) and single-input multiple-output (SIMO) systems, allowing for efficient utilization of available resources.

SM operates on the principle of exploiting the spatial domain, where multiple transmit antennas are employed to send information to the receiver using a combination of spatial indices. Unlike traditional MIMO techniques that transmit independent data streams on all transmit antennas simultaneously, SM uses a subset of transmit antennas to convey information.

The core idea behind SM is to map the information bits to both the active transmit antenna and its corresponding spatial index. Each transmit antenna is associated with a specific spatial position or index, which represents a unique spatial domain. This mapping process allows SM to transmit multiple independent streams of data using a combination of active transmit antennas and their associated spatial indices.

Let's dive into the detailed explanation of the SM process:

Transmitter Setup:

Multiple transmit antennas: The transmitter is equipped with multiple antennas, typically more than two, which can be arranged in a linear or planar array.
Spatial indices: Each transmit antenna is associated with a specific spatial index. These indices represent different spatial positions in the transmission system.
Mapping Scheme: A mapping scheme is used to associate the information bits with both the active transmit antenna and its corresponding spatial index.

Mapping Information Bits:

Information bit grouping: The input data stream is divided into groups of bits.
Spatial index selection: One or more bits from each group are used to select the active transmit antenna. The number of bits used for index selection depends on the number of transmit antennas.
Modulation of active antenna: The remaining bits in each group are used to modulate the active transmit antenna. Various modulation schemes, such as phase shift keying (PSK) or quadrature amplitude modulation (QAM), can be employed.

Spatial Modulation Process:

Antenna and index selection: The transmitter selects the active transmit antenna based on the spatial index bits. The selected antenna transmits the modulated signal.
Spatial index signaling: The spatial index bits are transmitted using the active antenna. This allows the receiver to determine which antenna is active at each transmission instant.
Data transmission: The modulated data bits are transmitted using the active antenna. Since only one antenna is active at a time, the transmitted signal power is concentrated on a single spatial domain.

Receiver Processing:

Antenna detection: The receiver performs antenna detection to identify the active antenna based on the spatial index signaling. This helps in determining the received signal's spatial domain.
Data detection: The received signal is processed to recover the transmitted data. The detection algorithms depend on the modulation scheme used for data transmission.

By employing SM, the transmitter can simultaneously transmit multiple independent streams of data using a smaller number of active antennas at any given time. This reduces the complexity and power consumption compared to traditional MIMO systems. At the receiver, spatial index detection and data detection algorithms are used to recover the transmitted information.

Overall, SM provides a promising approach for achieving higher data rates and spectral efficiency in wireless communication systems by exploiting the spatial dimensions and intelligently selecting active antennas and their corresponding spatial indices.