کنترل موجودی در سیستم های سریال تحت شناسایی فرکانس رادیویی

The widely adopted slap-and-ship radio frequency identification strategy provides valuable information to retailers. On the other hand, suppliers struggle to find benefits even though they are submerged with new data. Radio frequency identification provides complete visibility of their shipments, including the time and location of every pallet, case or even item. We provide a novel model relying on such data that is capable of producing better inventory and shipping control policies. We first propose a comprehensive inventory model for serial systems that captures both the supply and distribution information. We show that the underlying cost-to-go can be decomposed into two lower dimensional functions. In a special case, the optimal replenishment and shipping policies are base stock with respect to the underlying positions. In addition, we also analytically study the value of radio frequency identification in terms of the expected total minimum cost over a finite time horizon by introducing partial radio frequency deployment scenarios. Results indicate that additional cost reductions are possible with broader deployments.

A basic radio frequency identification (RFID) system includes two components: a transponder and an interrogator. A transponder is a tiny microcomputer consisting of a microchip, antenna and memory connecting these two. In the simplest form, the so-called passive RFID transponders, transponders are idle until woken up by an interrogator via radio wave signals. Interrogators are, therefore, constantly emitting signals to provide power to the transponders within their antenna's field of work. When a transponder receives a signal from an interrogator, it absorbs some of the radio energy to power itself and sends back a response, which among other data stored in its memory, includes the transponder's unique identification number. The interrogator decodes this information and passes it to information systems. In a typical RFID deployment within a supply chain, interrogators are mounted at critical locations. Every time goods affixed with transponders come within the read range of an interrogator, the location, time, and identification are recorded. Under normal conditions a typical interrogator may interrogate hundreds of transponders per second. One of the recent information technology advances is the adoption of RFID technology in inventory control systems. Early benefits earned from RFID deployments are inventory asset tracking, advance shipping notice, real-time order progress information for retailers, and real-time shipping visibility for suppliers. The additional RFID generated information could possibly result in improved inventory control policies and potential new business applications. One of the biggest setbacks to a wider RFID adoption is the lack of return of investment. Many entities in supply chains are overwhelmed with data generated from RFID deployment, yet this data is seldom used to enhance business intelligence. As an emerging auto data-capture enabler, RFID technology intrigues supply chain researchers and practitioners. Companies have rushed to develop RFID solutions without having a clear idea about the potential value of RFID to their business. One of the values of RFID in supply chains is derived from better supply chain visibility. An RFID deployment improves supply chain visibility; however, many benefits in inventory control are still untapped. The value of RFID obtained from labor cost reductions and similar basic benefits can be satisfactorily assessed by case studies. Empirical studies and proofs of concepts are of limited scope since they have to rely on existing processes and data. It is not clear how RFID can further reduce supply chain costs via improved visibility. Educated guesses are currently driving such estimates. Analytically modeling inventory control systems with an RFID deployment is critical to enhance our understanding of the value of RFID. Beyond replenishment inventory control on the supply side, the distribution side deals with shipping decisions. As is the case with the supply, RFID deployments yield real time visibility of shipments. To achieve such capability, it is typical to install portals with readers at important locations (e.g., in and/or outbound docks) and tag the corresponding goods. Consider an RFID mandate imposed by a retailer. A supplier places transponders on the products and ships them to the retailer's distribution centers, thus complying with the corresponding RFID mandate. Since typically transponders are affixed just before leaving the final facility of the supplier, this strategy is known as slap-and-ship. Clearly, to obtain further benefits from RFID, it is advised to push the tagging process further upstream in the supplier's own supply chain. The main drawback of slap-and-ship is the inability to produce return on investment. As already discussed, the retailer could benefit from continuously monitoring the inventory levels and outstanding order progress in its own chain. However, it is not clear how the supplier can benefit from the mandate even if real-time distribution information is provided by the retailer. This is a typical quote about such suppliers: “They (an apple supplier to Wal-Mart) know exactly what day and time the container was scanned through its portal, when it entered a distribution center and what day and time it went to the store. The company has yet to determine how best to use this data.”, Inbound Logistics, June 2006. The main objective of this research is to show how suppliers can benefit under such circumstances even under slap-and-ship. We assume a decentralized system where each entity in the chain acts independently. The main entity is an installation somewhere in the middle of the entire chain. The firm makes two decisions: (1) the replenishment decision from its own supplier and (2) the shipment decision how much to ship downstream. We study a single-product, multi-echelon serial supply chain system, in which the supplier streamlines both its replenishment and distribution processes by using the RFID data. We propose a dynamic programming model to capture the real time inventory information generated from an RFID deployment across the entire supply chain. The paper is organized as follows. A comprehensive inventory model is first presented in Section 2. In addition, we provide a special case with an instantaneous replenishment process. We apply multi-echelon techniques to decompose the proposed model into two sub-problems. The optimal control policy under certain conditions is characterized as the echelon base stock policy. The value of RFID in a serial distribution process is clearly identified and rigorously proved in Section 3 through discussions of partial RFID deployment scenarios. We conclude the introduction with a brief literature review. 1.1. Literature review Our models assume stochastic lead times. In standard single-stage stochastic inventory models, the lead time is considered either as a known deterministic constant or a random variable with known distribution. In these models (Kaplan, 1970; Nahmias, 1979; Ehrhardt, 1984) the lead time is assumed to be time-independent with known distribution. The non-crossover property is also assumed in order to make the study tractable. In our analysis, we borrow concepts from multi-echelon systems. The seminal work on the serial multi-echelon inventory problem was conducted by Clark and Scarf (1960). In their research, the global system is decomposed into separate sub-systems. At each echelon, it is optimal to follow the base stock policy with respect to the echelon inventory. RFID is the most promising technology providing complete and comprehensive supply chain visibility. It is a surprisingly simple computing and communication architecture since only two basic building blocks are needed—a tag and a reader (AIM Inc., 1999; Clampitt et al., 2006). We have already argued that RFID is an enabling technology for visibility that is assumed by our model. There are estimates about the value of RFID in supply chain management, including labor cost savings, reduced inventory holding costs, and stock-outs (Lee and Özer, 2007; Hardgrave, 2005). Most studies regarding RFID in inventory control concentrate on supply chain simulations (Lee et al., 2004; Fleisch and Tellkamp, 2005; Kang and Stanley, 2005). Bottani and Rizzi (2008) describe profitability of deploying RFID in a three-tier supply chain. They show by a real world case in a fast-moving consumer goods market the benefits of pallet-level tagging, and much more lenient results of case- and item-level tagging. Ustundag and Tanyas (2009) investigate impacts of different factors, such as product value, lead time, and uncertain demand on the supply chain cost performance at echelon levels in conjunction with RFID tagging. Among the few studies that analytically deal with RFID in inventory control, Song and Zipkin (1996) provide a modeling framework for the inventory control problem with supply information. While this study dates back to pre-era of modern RFID, it requires data available only through today's RFID deployments. The replenishment lead time is time-dependent and evolves over time. We borrow their modeling technique and enrich their study by focusing on the distribution side, thus dealing with two concurrent decisions. We also present results addressing the value of RFID in such distribution systems. Gaukler et al. (2008) quantify the benefits of RFID in the supply system of a retailer who faces uncertain demand and the option of emergency orders. They develop an order progress information model to study the optimal policies for both regular and emergency orders, under the assumption of a single outstanding order. Szmerekovsky and Zhang (2008) discuss impacts of item-level RFID tagging in a two-tier system under vendor managed inventory. First, the demand processes are characterized in both RFID and non-RFID systems. Then they study the control policies for each entity. Second, they study channel coordination efforts through sharing of the RFID costs by comparing centralized and decentralized systems. Atali et al. (2006) analytically study inventory inaccuracy, which is a joint effect of transaction errors, shrinkage, and misplacements. RFID yields more accurate inventory records and easier audits. Bottani et al. (2009) examine the impact of RFID on out-of-stocks of promotional items in the fast-moving consumer goods context. They show that by reducing the main causes of unavailability of sales through RFID can yield substantial savings. In addition, a reengineering process is exploited to compare the reduction of stock-outs. Results of an experiment suggest that RFID has the potential to reduce losses and improve profits in fast-moving consumer goods. New processes hinging on RFID are of particular interest. Expediting on the supply side is one such process that can benefit from RFID. Kim et al. (2006) address expediting strategies based on RFID data. Pricing strategies based on added value on goods are discussed in Schneider (2007). RFID is used as a technology to allow dynamic pricing.

After the initial lab experiments and case studies, the real breakthrough of RFID applications came with the RFID mandates imposed by Wal-Mart and the US Department of Defense. Most of their suppliers are required to apply at least pallet level RFID transponders to the products being shipped to selected distribution centers. The well-known slap-and-ship strategy provides valuable information and benefits to the retailers. However, it is much harder to identify a return on investment for suppliers. We first present a comprehensive inventory model and show that the underlying multivariate cost-to-go decomposes into two lower dimensional functions. Under certain assumptions, the optimal control policy for both replenishments and shipments is obtained. Furthermore, we analytically show that larger RFID deployments yield reduced overall expected cost. This clearly establishes that there is potential benefit of using RFID if novel processes are used. There are several important contributions of this work. Prior research mainly studies applications of RFID internally within a company or inventory control problems in a multi-firm setting with RFID supply information. This research is the first one to analytically study the inventory control policies with explicit RFID information at the distribution side. This is a non-trivial task since we have to simultaneously deal with two actions (replenishment and shipping quantities). Another contribution is, first, modeling a system with only a partial RFID deployment, and, second, comparing the expected cost of the resulting models with respect to the extent of the RFID deployment. Perhaps the most important contribution concerns the next generation business applications built on top of RFID data. We show that even by employing slap-and-ship, it is possible to generate additional value. This research is closing the gap between the ever increasing supply chain data and challenging analytical tools to process such information. The main contribution of our work is to establish models and policies for slap-and-ship that benefit suppliers. It is clear that in short-term slap-and-ship provides a quick and relatively low cost solution compared with a full-scale RFID deployment to achieve compliance with a retailer's mandate. On the other hand, experiences from slap-and-ship can shape suppliers’ future internal deployments and even further upstream, where suppliers can reap all the benefits from RFID. In this work, we show such possibility by an analytical approach exploiting the vast richness of RFID data. We first propose a comprehensive inventory model and then evaluate a serial distribution process with RFID deployments, which mimics the slap-and-ship processes of suppliers facing RFID mandates. The inventory control problem in the serial distribution chain is modeled as a dynamic program. Furthermore, the original problem is reduced in size to a simpler model without losing optimality. Based on this state reduction result, the optimal inventory control policy is the echelon base stock policy. It establishes that by knowing the downstream flow of goods through the distribution channel the supplier can improve decision making with respect to inventory control. The proposed comprehensive inventory model contains both supply and distribution information in serial systems. It asserts that armed with entire supply chain status information from using RFID, suppliers could better manage their internal and external processes and make integrated decisions that would improve their bottom line. The value of RFID in inventory control systems is also discussed in detail within the studied context. It is usually claimed that slap-and-ship is a cost-bearing solution. We argue that beyond the cost associated with slap-and-ship, suppliers could indeed find the benefits of RFID deployments downstream. We show analytically how RFID can improve the system performance in terms of the expected overall cost over a finite time horizon. The partial RFID deployment scenario with s+1 installations covered by RFID yields lower procurement and shipping costs than the costs based on s installations covered by RFID. The cost difference can be regarded as the true value of RFID in the system, setting aside the RFID system deployment and maintenance costs. The most important revelation and message of our paper is the fact that even by employing slap-and-ship, which is a basic deployment, benefits in inventory control are possible. Such benefits could offset the underlying costs and thus establish the elusive ROI for an RFID deployment. Clearly a positive ROI is not possible by simply slapping the tag and then shipping. An information system with analytical capabilities demonstrated here must be put together. RFID leaves an enormous trail of data that can be creatively analyzed and used to improve decision making. The results in Section 3 clearly demonstrate that wider RFID deployments bring additional benefits. Firms must carefully leverage deployment costs vs. benefits when deciding the scope of an RFID deployment. We demonstrated that additional benefits are definitely possible with broader deployments. A drawback of our study is that the actual deployment costs are not explicitly captured. We do not claim of showing a positive ROI, but without the analytical aspects presented herein, a positive ROI is definitely not possible under the slap-and-ship strategy. Many suppliers to Wal-Mart are struggling with the underlying costs of slap-and-ship. Through its power, Wal-Mart is able to dictate the RFID terms, while risking insolvency of smaller suppliers. Instead of these relentless pressures, Wal-Mart could more tightly collaborate with suppliers by using its tremendous IT resources and knowledge. To this end, it should show the suppliers how to gain benefits from its RFID mandate, and not only incur cost. By using the presented findings, the big-box retailer could show the suppliers how to improve inventory management simply by using the feedback data from Wal-Mart; thus not going deeper into the processes of the suppliers and more complex deployments of this pervasive technology. With the real-time information generated from RFID, many new research directions are possible. This research addresses a partial RFID deployment issue in order to study the value of RFID in inventory control. We assume RFID is deployed from the supplier downstream. An alternative setting not addressed here is to start deploying RFID at the point-of-sale and expanding it upward. It would be interesting to investigate the system differences between a forward and backward deployment. All partial RFID deployment scenarios in this work are based on perfect RFID read rates. This immediately raises the question of the impact of imperfect RFID read rates on system performance.