What is the difference between beamforming and spatial multiplexing?

Beamforming refers to focussing the signals in a particular direction. There are two types of beamforming

Reflection based

This can be seen in parabolic antennas which reflect the omnidirectional radiation from the source to a point (for example to a satellite in space or a base station on the ground)

All antennas are omnidirectional. We add reflecting elements to focus their energy where we want. Parabolic dishes are easiest to find but other antennas like yagi,horn etc also help in beam forming. Basically anything that reflects the signal in a particular direction can create a beam.

Beamforming is particularly important in point to point wireless backhauls. In these systems you want the signal to go in as straight a line as possible. Just like they would do if they were travelling in a fiber optic or an ethernet cable.

(That is why tower installation people try to find line of sight, so that once the beam is in place it is not obstructed by any other object like a building or a tree.)

Array based

Here we use the phase difference between multiple antenna elements to cut out the unwanted signals by destructive interference at some points while reinforcing the signals by constructive interference at others leading to a better signal in a particular direction. It works but it's not as efficient as reflection based passive beamforming and wastes energy. All antennas are omnidirectional. If the energy has been radiated why cut it out? Reflection may be passive but it saves energy. Even after phased array beamforming there is no guarantee of stronger signal.

(Keep in mind that beams are never straight lines but arcs that work in a sector instead of point to point. As the distance from the source increases the beam widens making the signal weaker.)

Multiplexing in general refers to the use of a resource by multiple consumers. In other words something that is shared by many.

Spatial multiplexing shares the space by dividing a signal into smaller streams ,transmitted at the same frequency, that are assembled at the receiver. This is one of the key ideas behind MIMO.

An obvious advantage is that since the data is divided into streams it can be delivered independently by the antenna closest to the user. In effect giving them the data over the strongest channel. When the user is close to all transmitting antennas his speed multiplies.

( Personally I remain skeptical of MIMO considering that the same effect can be achieved by using multiple devices each with their own antenna. Quantity beats quality in networking. Many base stations generating comparatively weaker signals are better than one or two stations generating a stronger /focussed signal. Of course this only holds when constructing and operating base stations becomes cheaper both in terms of investment and energy consumption. Effort spent in reducing cost and energy of individual stations will lead to a much better outcome than tinkering with channel access and data transmission. It is more likely however that I have misunderstood the core concept, so take my answer with atm grain of salt )

I’d love to hear your thoughts. Please don't hesitate to get in touch with me.

Akshat Jiwan Sharma

Strategy Consultant--Innovation/ Materials science/International relations/Telecommunications/Digital Transformation/Partnerships Mobile/whatsapp:+919654119771 email:getellobed@gmail.com

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