Macrodiversity

Key takeaways

Macrodiversity belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Macrodiversity to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Macrodiversity from memory before moving on to harder problems.

Reference excerpt

In the field of wireless communication, macrodiversity is a kind of space diversity scheme using several receiver or transmitter antennas for transferring the same signal. The distance between the transmitters is much longer than the wavelength, as opposed to microdiversity where the distance is in the order of or shorter than the wavelength. In a cellular network or a wireless LAN, macro-diversity implies that the antennas are typically situated in different base station sites or access points. Receiver macro-diversity is a form of antenna combining, and requires an infrastructure that mediates the signals from the local antennas or receivers to a central receiver or decoder. Transmitter macro-diversity may be a form of simulcasting, where the same signal is sent from several nodes. If the signals are sent over the same physical channel (e.g. the channel frequency and the spreading sequence), the transmitters are said to form a single-frequency network—a term used especially in the broadcasting world. The aim is to combat fading and to increase the received signal strength and signal quality in exposed positions in between the base stations or access points. Macro diversity may also facilitate efficient multicast services, where the same frequency channel can be used for all transmitters sending the same information. The diversity scheme may be based on transmitter (downlink) macro-diversity and/or receiver (uplink) macro-diversity.

Examples CDMA soft handoff: UMTS softer handoff. OFDM and frequency-domain equalization (FDE) based single-frequency networks (SFN) are a form of transmitter macrodiversity used in broadcasting networks such as DVB-T and DAB Dynamic single-frequency networks (DSFN), where a scheduling scheme adapts the SFN formations dynamically to traffic conditions and/or receiver conditions 802.16e macro diversity handover (MDHO) 3GPP long-term evolution (LTE) multicast-broadcast single-frequency network (MBSFN), making it possible to efficiently send the same data to many mobiles in adjacent cells. Cooperative diversity, for example 3GPP long term evolution (LTE) coordinated multipoint transmission/reception (CoMP), making it possible to increase the data rate to a mobile situated in the overlap of several base station transmission ranges.

Forms The baseline form of macrodiversity is called single-user macrodiversity. In this form, single user which may have multiple antennas, communicates with several base stations. Therefore, depending on the spatial degree of freedom (DoF) of the system, user may transmit or receive multiple independent data streams to/from base stations in the same time and frequency resource.

Single-user macrodiversity Uplink macrodiversity Downlink macrodiversity In next more advanced form of macrodiversity, multiple distributed users communicate with multiple distributed base stations in the same time and frequency resource. This form of configuration has been shown to utilize available spatial DoF optimally and thus increasing the cellular system capacity and user capacity considerably.

Multi-user macrodiversity Macrodiversity multiple access channel (MAC) Macrodiversity broadcast channel (BC)

Mathematical description

The macrodiversity multi-user MIMO uplink communication system considered here consists of N {\displaystyle \scriptstyle N} distributed single antenna users and n R {\displaystyle \scriptstyle n_{R}} distributed single antenna base stations (BS). Following the well established narrow band flat fading MIMO system model, input-output relationship can be given as

y = H x + n {\displaystyle \mathbf {y} =\mathbf {H} \mathbf {x} +\mathbf {n} }

where y {\displaystyle \scriptstyle \mathbf {y} } and

x {\displaystyle \scriptstyle \mathbf {x} } are the receive and transmit vectors, respectively, and H {\displaystyle \scriptstyle \mathbf {H} } and

n {\displaystyle \scriptstyle \mathbf {n} } are the macrodiversity channel matrix and the spatially uncorrelated AWGN noise vector, respectively. The power spectral density of AWGN noise is assumed to be N 0 {\displaystyle \scriptstyle N_{0}} . The i , j {\displaystyle \scriptstyle i,j} th element of H {\displaystyle \scriptstyle \mathbf {H} } , h i j {\displaystyle h_{ij}}

represents the fading coefficient (see Fading) of the i , j {\displaystyle \scriptstyle i,j} th constituent link which in this particular case, is the link between

j {\displaystyle \scriptstyle j} th user and the i {\displaystyle \scriptstyle i} th base station. In macrodiversity scenario,

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Macrodiversity

Start with the simplest possible case. Write down what Macrodiversity claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Macrodiversity before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Macrodiversity ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Macrodiversity

In research: Macrodiversity appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Macrodiversity in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Macrodiversity is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antennas, Radio resource management, so understanding it makes those chapters shorter.
In everyday life: Look for Macrodiversity outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Macrodiversity in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Macrodiversity means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Macrodiversity out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Macrodiversity in simple terms?

In the field of wireless communication, macrodiversity is a kind of space diversity scheme using several receiver or transmitter antennas for transferring the same signal. The distance between the transmitters is much longer than the wavelength, as opposed to microdiversity where the distance is in…

Why does Macrodiversity matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Macrodiversity?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Macrodiversity.