Femtocells will initially operate as part of the mobile operators network and reuse the same billing mechanisms and systems. This allows any user (including roaming visitors) to use femtocells and be charged in the same way.
Here we give a brief introduction on how Mobile Billing works and then explain the implications of billing for Femtocells
How Mobile Billing Works
Customers almost always have either prepaid or postpaid accounts with their operator.
Postpaid accounts capture usage information from the network in the form of billing records, or call detail records (CDRs). One or more CDRs may be generated for each telephone call or service used. These are streamed or batch processed into large data processing centres which “rate” (ie work out the price) for each service delivered. Often a regular (eg monthly) bill is produced, which handles more complex features such as recurring charges, volume discounts and other special cases.
Once the postpaid bill is produced, this is passed across to the charging and settlement systems which collect the money for the bill, either as a direct debit from the customers bank account or other payment mechanism. The collections system tracks that bills are being paid and takes corrective action when this is not the case.
This process is quite secure as long as the devices which generate the billing records (CDRs) are under the control of the operator, and their can be no doubt that the service is being used by the genuine customer. The operator performs credit checks to limit the risk of unpaid bills, but would expect to write-off some unpaid debts.
Prepaid accounts authorise each transaction before it takes place. This requires “real-time” systems directly connected to the network which are queried before each call, text or data service is used. The prepaid system must “rate” (i.e. calculate the price) for each call and check and reserve the account balance before authorising it to proceed.
Whilst this is more complex and demanding to implement than postpaid billing, it avoids the risk of unpaid bills and significant improves the cashflow for the operator because payment is made in advance. It is also secure, as long as devices which query the prepaid system are all under the control of the operator, and their can be no doubt that the service is being used by the genuine customer. However, this method is considered less appropriate for corporate and high spending customers, who might otherwise limit their spending.
Billing for Femtocells
The current architecture for femtocells involves routing all calls through to the mobile operator’s core network, and thus using the same systems as for any other service. This provides transparent access for both prepaid and postpaid users, including visitors roaming from another network/country.
Customers who install femtocells are offered favourable rates when making/receiving calls through it. This includes “unlimited” calling for a flat fee (e.g. Sprint Airave offers unlimited calls to other mobiles and US landlines for $15/month), but premium numbers, international calls and data services may be charged at standard rates.
This is achieved by recording the cellsite identity in the billing record and taking this into account when rating (ie calculating the price) for the call. Most prepaid systems also have the capability to use the cell identity in this way. These features have been used in the past by operators who offered “Home Zone” tariff plans, whereby calls made from the customers house (or workplace) were charged at a preferred rate. This was based on comparing the cellsite identity for each call with the cellsites known to cover the customers “home zone” area. However, often these areas would be quite large and thus customers qualified for lower rates on many of their calls. The femtocell solution improves on this due to the targeted range (say up to 200m) covered.
Advice of Charge
It is important to avoid confusion or “bill shock” where customers are charged for services they thought were free/reduced price. Therefore, there needs to be a mechanism for the customer to know that the call is being made/received via the femtocell and thus benefits from the local rate.
In the future, phones may be able to display an icon or show another indication that they are in their local femtocell area. Dual-mode systems which use WiFi require a different phone and these often include an indicator for when operating in WiFi mode. Initial solutions, such as the Sprint Airave made by Samsung, provide a short audible tone at the start of each call for this purpose.
When used for data services (ie internet access) it will not be efficient or cost effective for the operator to route all the traffic through their network. Offload solutions have been proposed whereby all of the functionality of the core packet network is integrated into the local femtocell, and thus can directly connect from the femtocell to the external internet. This is likely to require losing some of the security by not being able to control the device. It is important that such solutions do not compromise the security and integrity of the billing system, either by inadvertently overcharging a subscriber or opening an unintentional loophole for free services.
Clarity of billing is also important to avoid causing customer confusion. Therefore billing plans and tariffs must be easily understood and implemented.