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Difference between Cellular network and Cell-free network

This page compares Cellular network and Cell-free network and mentions difference between Cellular network and Cell-free network.

Introduction:
In traditional cellular network, each area is divided into regions i.e. cells. BSs (Base Stations) are deployed in each of these cells. Single BS serves many users with wide coverage. All the BSs are connected together and to Core Network (CN) using backhaul connectivity.

In cell free network, entire area is served by many APs (Access Points) and there is no concept of cells. All the APs are connected with CPU (Central Processing Unit). All the CPUs are interfaced with Core Network (CN). Cell free network consists of antenna units, APUs (Antenna Processing Units), CPUs (Central Processing Units). Many APs serve all the users in their area of influence. One user is served by multiple APs in cell free network.

Cellular network

cellular network

The figure-1 depicts cellular network. BSs are interfaced as per various configurations such as star, mesh etc. They are interfaced with PSTN (Public Switched Telephone Network) , MSCs (Mobile Switching Centres) and PSDN (Public Switched Data Network) in the backhaul. The common cellular networks are GSM, CDMA, LTE, 5G etc. Refer Pros and Cons of Cellular Network and Cellular Communication tutotial >>.

Cell-free network

The figure-2 depicts Cell free network. As shown, Cell-Free Massive MIMO consists of Access Points (APs) and central processor connected by fronthaul. APs are deployed which are scattered over the coverage area. Each of the APs are connected using fronthaul i.e. wires to a central processing unit. The central processor controls all the APs. All the APs serve all the surrounding users and there are no cell boundaries as in cellular network. Hence the name "cell-free" for such network architecture.

Cell Free Massive MIMO Architecture

In this architecture, many antennas are distributed geographically instead of co-location in BS (Base Station). These antennas are known as APs (Access Points). These APs operate jointly to serve subscribers in same time/frequency resources. APs work together synchronously and coherently. APs function as a massive MIMO BS which are coordinated by one or more Central processors using fronthaul network. Refer Cell Free network >> for Pros and Cons of cell free massive MIMO architecture.

Difference between Cellular network and Cell-free network

Following table mentions difference between cellular network and cell-free network.

Parameters Cellular network Cell free network
• Definition In cellular network, area to be served is divided into sub-areas called cells. APs are deployed in each of these cells. APs communicate with each other using backhaul. APs are interfaced with core network (CN) to serve different types of users. No concept of cells. Entire area is not divided and APs are spread across entire area. APs are connected together and to CPU (Central Processing Unit) using cables (called fronthaul).
• Interference Interference between neighbouring cells. Interference can be controlled by fractional spectrum reuse or by reduction in transmit power. No cells and hence there is no interference.
• Visibility APs in the form of cell tower antennas are visible. APs are not visible to users.
• Distance Distance between APs (i.e. cell tower antennas) and users is larger. Distance from APs to users is smaller.
• Signal strength The signal variation is large. It leads to weak signal to some users. The signal variation is less due to closeness of users from APs. Hence signals usually is strong enough to almost all the users.
• Blockage of signal Sensitive to signal blocking Not sensitive to signal blocking due to use of metasurfaces (i.e. Intelligent reflecting surfaces) and deployment of APs everywhere.
• Service quality Non uniform service, users at the edges do not get same performance as users near to the cell tower. This is not good for data calls but enough for voice calls. Uniform service quality in the entire network.
• Antenna design Directive antenna (~ three numbers) with higher directivity are used in 4G LTE network. 5G uses massive MIMO antennas (~ 64) which provides strong and adaptive directivity. Nearby users get good performance but users at edges get poor performance. All the users get good performance due to closeness of APs due to availability of distributed antennas (omni-directional) everywhere using radio stripes.
• Cooling Required due to high power transmission to cover longer distances due to large signal strength variations Does not require cooling.
• Architecture design Network centric type design User centric design, each user is served by all APs in its area of influence or significance.
• Joint signal decoding by multiple APs Not present Present
• Performance Poor compare to cell free case 90% improvement in performance (i.e. CDF versus spectral efficiency) in centalized version
• Cost Expensive due to higher cost of Base Stations Cheaper due to less costly APs, radio stripes are invented to fulfill this.
• Control complexity Lesser Higher, minimized using radio stripes based new architecture in which APUs(Antenna Processing units) take care of antenna units rather than single CPU (Central Processing Unit).
• Wireless connectivity performance Good Better, more reliable than traditional existing cellular networks.
• Example Setup 1. Massive MIMO using 4 APs with 100 antennas each
2. OR small cells having same AP locations as in cell free scenario
400 APs on square grid (e.g. 1km by 1km) using either centralized or distributed processing



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