## 3 Existing Method  
In this section, we first explain the procedure of the pull-type RevAuc that uses only cellular communication (Figure 3), which we call the existing method in this paper. This method is based on the method of MCS using RevAuc described in previous studies [8; 9]. We assume that sensing data service users can send a data request for any location (POI) to a server at any time. We make two assumptions to reduce cellular traffic in RevAuc for the existing method. We assume that the server sends a bid invitation for a currently effective data request to a mobile host if the server determines that the mobile host is highly likely to provide the requested data in pull-type RevAuc. This assumption is for reducing cellular traffic for useless Bid Invitation messages. We assume that a common bid evaluation function is defined so that the server and mobile hosts calculate the evaluation score of a bid based on the location of a mobile host, the time when it obtains data, and the reward offered in the bid. The server selects a mobile host that tendered the bid with the highest evaluation score as a successful bidder. Each mobile host calculates the evaluation score of the bid that it can tender. If the evaluation score of a bid calculated by a mobile host is more than zero, the mobile host tenders the bid so that cellular traffic for useless Bids messages can be reduced. 1. Each mobile host sends a Bid Invitations Query message, which includes the location of the mobile host, to a server periodically with a cycle \(T_{q}\). This message serves to trigger a bid invitation from the server. 2. The server selects data requests that it has received recently and matches the Bid Invitations Query message based on the location of the mobile host included in the query message. The server sends multiple bid invitations in a single Bid Invitations message to the mobile host. Each bid invitation in the message includes the data request (data request identifier (ID), POI, and specification of data to be obtained (e.g., the type of sensor to be used)), the maximum reward to be paid, and the time when the successful bidder will be determined (auction end time). In this study, we assume that the server selects a successful bidder for a data request when time \(T_{L}\) has passed after the data request is received by the server. \(T_{L}\) is longer than the time \(T_{q}\), which is the duration in which the request is effective. 3. The mobile host calculates the reward it will offer for the bid invitations in the Bid Invitations message. It sends bids to the server by a Bids message. Each bid in the message includes the data request ID, bidding mobile host's ID, expected location and time for data acquisition by the mobile host, specification of the data to be obtained, and the reward (i.e., bid price) it offers to the server for the data. We assume that the mobile hosts and the server use the same bid evaluation function. 4. For each data request, the server selects a successful bidder mobile host that sent the bid with the highest evaluation score among mobile hosts that have sent a bid within time \(T_{q}\) after the data request was received. Then, the server sends a Bid Result message, which asks the mobile host to obtain and transmit the data, to the successful bidder mobile host. The Bid Result message includes the content of the bid, as described in step (3), that was sent with the Bids message from the successful bidder. 5. If a mobile host that has sent a bid to the server has not received a Bid Result message from the server by the auction end time included in the Bid Invitation, it knows that it was not selected as the successful bidder. If a mobile host receives a Bid Result message, it sends a Data message to the server after it obtains the requested data. The Data message includes the data request ID and requested data. After receiving a Data message, the server processes the received data to fulfill the original data request.